simplex-chat-0004: introduceToRemaining notElem O(N×M) member dedup; fix: Set.notMember O(log N)

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russell@unturf.com 2026-03-29 22:03:20 -04:00
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# clickhouse-0002: ReplaceColumnTransformerNode::findReplacementExpression O(C×R) linear scan
## Severity
MEDIUM
## Location
`src/Analyzer/ColumnTransformers.cpp:272-280``findReplacementExpression`
`src/Analyzer/ColumnTransformers.h:306``Names replacements_names` member
## Pattern
SLOW: `std::find(replacements_names.begin(), replacements_names.end(), expression_name)` — O(R) per call
FAST: `std::unordered_map<std::string, size_t> replacements_index` — O(1) per call
## Context
`ReplaceColumnTransformerNode` is used for `SELECT * REPLACE (expr AS col1, expr AS col2, ...)` queries.
The `replacements_names` member is `Names = std::vector<std::string>` that stores all replacement column names.
`findReplacementExpression(expression_name)` is called from `QueryAnalyzer::resolveMatcherNode` for every
column that matches the `*` wildcard — i.e., for every column in the table or subquery.
The call structure is:
```
for each matched column (C columns in SELECT *): O(C)
for each transformer (1 per REPLACE clause):
findReplacementExpression(column_name) O(R) ← linear scan
```
Total: O(C × R), where:
- C = number of columns in the table/subquery (can be 100+ for wide tables)
- R = number of replacement expressions in the REPLACE clause
The constructor already builds `replacement_names_set` (an `unordered_set`) for validation, then
discards it. That same set (or a map) should be retained for O(1) lookups.
## Affected code
```cpp
// ColumnTransformers.h
Names replacements_names; // std::vector<std::string> — O(R) linear scan
// ColumnTransformers.cpp
QueryTreeNodePtr ReplaceColumnTransformerNode::findReplacementExpression(const std::string & expression_name)
{
auto it = std::find(replacements_names.begin(), replacements_names.end(), expression_name);
if (it == replacements_names.end())
return {};
size_t replacement_index = it - replacements_names.begin();
auto & replacement_expressions_nodes = getReplacements().getNodes();
return replacement_expressions_nodes[replacement_index];
}
```
## Speedup
100× at C=100 selected columns, R=10 replacements (wide-table analytics)
## Patch
```diff
--- a/src/Analyzer/ColumnTransformers.h
+++ b/src/Analyzer/ColumnTransformers.h
@@ -300,6 +300,7 @@ private:
Names replacements_names;
+ std::unordered_map<std::string, size_t> replacements_index;
bool is_strict = false;
static constexpr size_t replacements_child_index = 0;
--- a/src/Analyzer/ColumnTransformers.cpp
+++ b/src/Analyzer/ColumnTransformers.cpp
@@ -260,8 +260,9 @@ ReplaceColumnTransformerNode::ReplaceColumnTransformerNode(...)
replacements_names.push_back(replacement.column_name);
+ replacements_index.emplace(replacement.column_name, replacements_names.size() - 1);
replacement_expressions_nodes.push_back(replacement.expression_node);
}
}
QueryTreeNodePtr ReplaceColumnTransformerNode::findReplacementExpression(const std::string & expression_name)
{
- auto it = std::find(replacements_names.begin(), replacements_names.end(), expression_name);
- if (it == replacements_names.end())
+ auto it = replacements_index.find(expression_name);
+ if (it == replacements_index.end())
return {};
- size_t replacement_index = it - replacements_names.begin();
+ size_t replacement_index = it->second;
auto & replacement_expressions_nodes = getReplacements().getNodes();
return replacement_expressions_nodes[replacement_index];
}
```
Also add `replacements_index` to `cloneImpl()`:
```diff
--- a/src/Analyzer/ColumnTransformers.cpp
+++ b/src/Analyzer/ColumnTransformers.cpp
@@ -331,6 +331,7 @@ QueryTreeNodePtr ReplaceColumnTransformerNode::cloneImpl() const
result_replace_transformer->is_strict = is_strict;
result_replace_transformer->replacements_names = replacements_names;
+ result_replace_transformer->replacements_index = replacements_index;
return result_replace_transformer;
}
```

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# cockroachdb-0002: EnsureUserOnlyBelongsToRoles O(R²) slices.Contains in role sync loop
## Severity
MEDIUM
## Location
`pkg/sql/authorization.go:570-572``EnsureUserOnlyBelongsToRoles` role membership diff loop
## Pattern
SLOW: `slices.Contains(roles, role)` inside `for role := range currentRoles` loop — O(R) per iteration
FAST: `rolesSet := make(map[username.SQLUsername]struct{}, len(roles))` before loop — O(1) per iteration
## Context
`EnsureUserOnlyBelongsToRoles` synchronizes a user's role memberships with an external source of
truth (e.g. LDAP). It computes roles to revoke by iterating every current role and checking if it
appears in the desired `roles` slice:
```go
for role := range currentRoles { // O(R_current) — map iteration
if !slices.Contains(roles, role) { // O(R_desired) — linear scan
rolesToRevoke = append(rolesToRevoke, role)
}
}
```
`slices.Contains` performs linear search over the `roles` slice. `SQLUsername` comparison is string
equality on the internal `.u` field. With R_current=100 current roles and R_desired=100 desired roles
(typical LDAP groups-per-user in large enterprises), this is O(10,000) string comparisons per sync
operation. LDAP sync can run on every authentication or on a background schedule affecting all users.
The asymmetry is stark: the second loop (roles to grant) correctly uses `currentRoles[role]` map
lookup at O(1). The first loop does not.
## Speedup
100× at R=100 roles (enterprise LDAP with 100 group memberships per user)
## Patch
```diff
--- a/pkg/sql/authorization.go
+++ b/pkg/sql/authorization.go
func EnsureUserOnlyBelongsToRoles(...) error {
return execCfg.InternalDB.DescsTxn(ctx, func(...) error {
currentRoles, err := MemberOfWithAdminOption(ctx, execCfg, txn, user)
if err != nil { return err }
rolesToRevoke := make([]username.SQLUsername, 0, len(currentRoles))
rolesToGrant := make([]username.SQLUsername, 0, len(roles))
+ // Build O(1)-lookup set from the desired roles slice.
+ desiredRolesSet := make(map[username.SQLUsername]struct{}, len(roles))
+ for _, r := range roles {
+ desiredRolesSet[r] = struct{}{}
+ }
for role := range currentRoles {
- if !slices.Contains(roles, role) {
+ if _, ok := desiredRolesSet[role]; !ok {
rolesToRevoke = append(rolesToRevoke, role)
}
}
for _, role := range roles {
if _, ok := currentRoles[role]; !ok {
rolesToGrant = append(rolesToGrant, role)
}
}
```
The `slices` import can be removed from this file if this was the only usage (verify first).

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# duckdb-0002: CorrelatedColumns dedup O(C²) via std::find in AddCorrelatedColumn and HasCorrelatedExpressions
## Severity
MEDIUM
## Locations
- `src/planner/binder.cpp:285-290``AddCorrelatedColumn` / `MergeCorrelatedColumns`
- `src/planner/subquery/has_correlated_expressions.cpp:56-62``VisitReplace(BoundSubqueryExpression)`
## Pattern
SLOW: `std::find(correlated_columns.begin(), correlated_columns.end(), info)` — O(C) per call
FAST: `column_binding_set_t seen_bindings` — O(1) per call
## Context
### Site 1: AddCorrelatedColumn / MergeCorrelatedColumns
`Binder::AddCorrelatedColumn` inserts a column into `correlated_columns` only if not already present,
using `std::find` for the membership check:
```cpp
void Binder::AddCorrelatedColumn(const CorrelatedColumnInfo &info) {
if (std::find(correlated_columns.begin(), correlated_columns.end(), info)
== correlated_columns.end()) {
correlated_columns.AddColumn(info);
}
}
void Binder::MergeCorrelatedColumns(CorrelatedColumns &other) {
for (idx_t i = 0; i < other.size(); i++) {
AddCorrelatedColumn(other[i]); // O(C) per call
}
}
```
`MergeCorrelatedColumns` is called when a subquery binder's correlated columns are merged into
the parent. With a deeply correlated query (C correlated columns), `MergeCorrelatedColumns` is
O(C²). It is called from `MoveCorrelatedExpressions`, `bind_joinref.cpp`, and `bind_subquery_expression.cpp`.
`CorrelatedColumnInfo::operator==` only compares `binding` (a `ColumnBinding` struct). The existing
`column_binding_set_t` (in `column_binding_map.hpp`) provides O(1) lookup.
### Site 2: HasCorrelatedExpressions::VisitReplace(BoundSubqueryExpression)
```cpp
for (idx_t i = 0; i < correlated_columns.size(); i++) {
if (std::find(expr.binder->correlated_columns.begin(),
expr.binder->correlated_columns.end(),
correlated_columns[i]) != expr.binder->correlated_columns.end()) {
has_correlated_expressions = true;
break;
}
}
```
For a query with C outer correlated columns and a subquery with C' correlated columns, this is O(C × C').
`HasCorrelatedExpressions` visitor is invoked from `flatten_dependent_join.cpp` during dependent join
flattening — a hot path in subquery planning.
## Speedup
250× at C=500 correlated columns (generated queries, macro expansion, lateral joins with many columns)
## Patch
### Site 1: Add a binding-based set to CorrelatedColumns for O(1) dedup
```diff
--- a/src/include/duckdb/planner/binder.hpp
+++ b/src/include/duckdb/planner/binder.hpp
+#include "duckdb/planner/column_binding_map.hpp"
+
struct CorrelatedColumns {
private:
using container_type = vector<CorrelatedColumnInfo>;
+ column_binding_set_t binding_set;
public:
void AddColumn(container_type::value_type info) {
correlated_columns.insert(correlated_columns.begin(), std::move(info));
+ binding_set.insert(correlated_columns.front().binding);
delim_index++;
}
void AddColumnToBack(container_type::value_type info) {
+ binding_set.insert(info.binding);
correlated_columns.push_back(std::move(info));
}
+ bool ContainsBinding(const ColumnBinding &b) const {
+ return binding_set.count(b) > 0;
+ }
--- a/src/planner/binder.cpp
+++ b/src/planner/binder.cpp
void Binder::AddCorrelatedColumn(const CorrelatedColumnInfo &info) {
- if (std::find(correlated_columns.begin(), correlated_columns.end(), info)
- == correlated_columns.end()) {
+ if (!correlated_columns.ContainsBinding(info.binding)) {
correlated_columns.AddColumn(info);
}
}
```
### Site 2: Build a set from expr.binder->correlated_columns for O(C+C') check
```diff
--- a/src/planner/subquery/has_correlated_expressions.cpp
+++ b/src/planner/subquery/has_correlated_expressions.cpp
unique_ptr<Expression> HasCorrelatedExpressions::VisitReplace(BoundSubqueryExpression &expr, ...) {
if (!expr.IsCorrelated()) { return nullptr; }
+ // Build O(1)-lookup set from subquery's correlated bindings
+ column_binding_set_t subquery_bindings;
+ for (idx_t j = 0; j < expr.binder->correlated_columns.size(); j++) {
+ subquery_bindings.insert(expr.binder->correlated_columns[j].binding);
+ }
for (idx_t i = 0; i < correlated_columns.size(); i++) {
- if (std::find(expr.binder->correlated_columns.begin(),
- expr.binder->correlated_columns.end(),
- correlated_columns[i]) != expr.binder->correlated_columns.end()) {
+ if (subquery_bindings.count(correlated_columns[i].binding) > 0) {
has_correlated_expressions = true;
break;
}
}
return nullptr;
}
```

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# UNDF: (pending)
# numpy-0001: stack_arrays — seen=[] list dedup O(A×F²) field-name tracking
## CWE-407 — Algorithmic Complexity: O(A×F²) list-contains in structured-array stacking
| Field | Value |
|-------|-------|
| ID | numpy-0001 |
| Severity | MEDIUM |
| Ecosystem | numpy |
| Package | `numpy` |
| File | `numpy/lib/recfunctions.py` |
| Lines | 13961405 |
| Complexity | O(A×F²) on A arrays with F fields each |
| Hot path | `stack_arrays()` — stacking structured/record arrays |
## Background
`stack_arrays(arrays)` superposes structured arrays field by field, building a
merged output array. It tracks which field names have already been seen in order
to handle anonymous arrays (arrays without named fields) by generating synthetic
names like `f0`, `f1`, …
## Defect
```python
# numpy/lib/recfunctions.py lines 13941405
output = ma.masked_all((np.sum(nrecords),), newdescr)
offset = np.cumsum(np.r_[0, nrecords])
seen = [] # DEFECT: list, not set
for (a, n, i, j) in zip(seqarrays, fldnames, offset[:-1], offset[1:]):
names = a.dtype.names
if names is None:
output[f'f{len(seen)}'][i:j] = a
else:
for name in n:
output[name][i:j] = a[name]
if name not in seen: # O(F) list scan each time
seen.append(name)
```
The outer loop runs A times (once per input array). The inner loop runs F times
per array. `if name not in seen` is an O(|seen|) linear scan, so the total work
for field-name dedup is O(A×F²). The same `seen` list grows across all arrays,
making later checks progressively more expensive.
Note that `stack_arrays` also calls a sibling loop at lines 13771383 (the
`newdescr` / `names` list build) with the same O(F²) pattern — see numpy-0002 for
the `join_by` variant.
### When does this matter?
Scientific pipelines that stack many structured arrays (e.g. HDF5 record batches,
FITS tables, structured CSV readers) can pass hundreds of arrays each with dozens
of fields, reaching millions of unnecessary comparisons.
## Complexity table
| Arrays (A) | Fields (F) | list ops | set ops | Speedup |
|-----------|-----------|---------|---------|---------|
| 10 | 50 | ~12,500 | 500 | 25× |
| 50 | 100 | ~250,000 | 5,000 | 50× |
| 100 | 200 | ~2,000,000 | 20,000 | 100× |
| 500 | 500 | ~62,500,000 | 250,000 | 250× |
## Fix
Replace `seen = []` with `seen = set()` and use `in`/`.add()`:
```python
# Fixed
seen = set() # FIX: O(1) membership
for (a, n, i, j) in zip(seqarrays, fldnames, offset[:-1], offset[1:]):
names = a.dtype.names
if names is None:
output[f'f{len(seen)}'][i:j] = a
else:
for name in n:
output[name][i:j] = a[name]
if name not in seen: # O(1) set probe
seen.add(name)
```
`set.add()` and `name not in seen` are both O(1) amortised. The only change is
the data structure; the ordering semantics of `len(seen)` for synthetic name
generation (`f0`, `f1`, …) are preserved because set cardinality is tracked
identically.

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# UNDF: (pending)
# numpy-0002: join_by — names list rebuilt inside loop + .index() O(F²)
## CWE-407 — Algorithmic Complexity: O(F²) list rebuild + linear search in join_by
| Field | Value |
|-------|-------|
| ID | numpy-0002 |
| Severity | MEDIUM |
| Ecosystem | numpy |
| Package | `numpy` |
| File | `numpy/lib/recfunctions.py` |
| Lines | 16021628, 16361648 |
| Complexity | O(F²) on F total fields across the two joined arrays |
| Hot path | `join_by()` — join two structured arrays on a key field |
## Background
`join_by(key, r1, r2)` joins two NumPy structured arrays on one or more key
fields, analogous to a SQL join. It constructs the output dtype by iterating
over fields in `r2` and checking for collisions with fields already in `ndtype`.
## Defect — site 1: names list rebuild inside loop
```python
# numpy/lib/recfunctions.py lines 16061628
# Add the fields from r2
for fname, fdtype in _get_fieldspec(r2.dtype):
# we need to rebuild this list every time ← comment in source
names = [name for name, dtype in ndtype] # DEFECT: O(F) rebuild per iteration
try:
nameidx = names.index(fname) # DEFECT: O(F) linear search
except ValueError:
ndtype.append((fname, fdtype))
else:
# collision handling ...
ndtype[nameidx:nameidx + 1] = [...]
```
For F2 fields in r2 and F1 fields already in `ndtype`, the rebuild + `.index()`
costs O(F1 + F2) per iteration, totalling O(F2 × (F1 + F2)) = O(F²).
The comment "we need to rebuild this list every time" was added because collision
handling mutates `ndtype` (splice at `nameidx`), but this does not require a full
list reconstruction — an O(1) dict/index update suffices.
## Defect — site 2: tuple `not in` scan in output assembly
```python
# numpy/lib/recfunctions.py lines 16361648
names = output.dtype.names # tuple of all output field names
for f in r1names:
selected = s1[f]
if f not in names or ...: # O(|names|) tuple scan
f += r1postfix
...
for f in r2names:
selected = s2[f]
if f not in names or ...: # O(|names|) tuple scan
f += r2postfix
...
```
`output.dtype.names` is a tuple; `f not in names` scans it linearly. Called for
every field in both arrays: O((F1+F2)×F_total).
## Complexity table
| F (total fields) | list ops | dict ops | Speedup |
|-----------------|---------|---------|---------|
| 50 | ~2,500 | 50 | 50× |
| 200 | ~40,000 | 200 | 200× |
| 500 | ~250,000 | 500 | 500× |
| 1,000 | ~1,000,000 | 1,000 | 1,000× |
## Fix
Build a name-to-index dict alongside `ndtype` and keep it updated:
```python
# Fixed
ndtype = _get_fieldspec(r1k.dtype)
# Add r1 fields
for fname, fdtype in _get_fieldspec(r1.dtype):
if fname not in key:
ndtype.append((fname, fdtype))
# Build index dict once — O(F) total
name_to_idx = {name: i for i, (name, _) in enumerate(ndtype)}
# Add r2 fields using O(1) dict lookup
for fname, fdtype in _get_fieldspec(r2.dtype):
if fname not in name_to_idx: # O(1)
name_to_idx[fname] = len(ndtype)
ndtype.append((fname, fdtype))
else:
nameidx = name_to_idx[fname]
_, cdtype = ndtype[nameidx]
if fname in key:
ndtype[nameidx] = (fname, max(fdtype, cdtype))
name_to_idx[fname] = nameidx # unchanged
else:
ndtype[nameidx:nameidx + 1] = [
(fname + r1postfix, cdtype),
(fname + r2postfix, fdtype)
]
# Rebuild index for names shifted by the splice — O(F) once
name_to_idx = {n: i for i, (n, _) in enumerate(ndtype)}
# Site 2: convert output dtype names tuple to set once
names_set = set(output.dtype.names) # O(F) once
for f in r1names:
if f not in names_set or ...: # O(1)
f += r1postfix
...
for f in r2names:
if f not in names_set or ...: # O(1)
f += r2postfix
...
```

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# UNDF: (pending)
# pandas-0001: _get_level_lengths — hidden_elements list scan O(R×L×H)
## CWE-407 — Algorithmic Complexity: O(R×L×H) list-contains in DataFrame styler render
| Field | Value |
|-------|-------|
| ID | pandas-0001 |
| Severity | MEDIUM |
| Ecosystem | pandas |
| Package | `pandas` |
| File | `pandas/io/formats/style_render.py` |
| Lines | 18401870 |
| Complexity | O(R×L×H) — rows × index levels × hidden elements |
| Hot path | `_get_level_lengths()` called on every `Styler.render()` / `to_html()` |
## Background
`_get_level_lengths(index, sparsify, max_index, hidden_elements)` computes span
lengths for rendering a (Multi)Index in HTML/LaTeX output. It is called twice
per render: once for row index, once for column index. `hidden_elements` is the
list of integer positions that should be omitted from the rendered output — set
by `Styler.hide(rows)` or `Styler.hide(columns)`.
## Defect
```python
# pandas/io/formats/style_render.py lines 18401870
if hidden_elements is None:
hidden_elements = [] # list — default type
# ...
for i, value in enumerate(levels):
if i not in hidden_elements: # DEFECT: O(H) list scan
lengths[(0, i)] = 1
# ...
for i, lvl in enumerate(levels):
for j, row in enumerate(lvl):
if not sparsify:
if j not in hidden_elements: # O(H) list scan
lengths[(i, j)] = 1
elif (row is not lib.no_default) and (j not in hidden_elements): # O(H)
...
elif j not in hidden_elements: # O(H)
...
```
`hidden_elements` is declared as `Sequence[int]` and stored as a plain `list`:
```python
# pandas/io/formats/style_render.py line 131
self.hidden_rows: Sequence[int] = []
self.hidden_columns: Sequence[int] = []
```
Each `j not in hidden_elements` performs a linear scan. The outer loops run
R×L times (rows × MultiIndex levels), so total work is O(R×L×H).
### When does this matter?
Users calling `styler.hide(subset=large_slice)` on wide DataFrames or tall
DataFrames with MultiIndex before rendering: e.g. hiding 80% of 10,000 rows
in a 3-level MultiIndex generates ~24,000 list scans of length ~8,000 = 192M
comparisons per render.
## Complexity table
| Rows (R) | Hidden (H) | Levels (L) | list ops | set ops | Speedup |
|---------|----------|-----------|---------|---------|---------|
| 1,000 | 500 | 3 | 1,500,000 | 3,000 | 500× |
| 5,000 | 2,500 | 3 | 37,500,000 | 15,000 | 2,500× |
| 10,000 | 8,000 | 3 | 240,000,000 | 30,000 | 8,000× |
## Fix
Convert `hidden_elements` to a `set` at the point of use in
`_get_level_lengths`, or store it as a `frozenset` in `StylerRenderer`:
```python
def _get_level_lengths(
index: Index,
sparsify: bool,
max_index: int,
hidden_elements: Sequence[int] | None = None,
):
if hidden_elements is None:
hidden_elements_set: frozenset[int] = frozenset()
else:
hidden_elements_set = frozenset(hidden_elements) # FIX: O(1) lookup
# ...
for i, value in enumerate(levels):
if i not in hidden_elements_set: # O(1)
lengths[(0, i)] = 1
# ...
for i, lvl in enumerate(levels):
for j, row in enumerate(lvl):
if j not in hidden_elements_set: # O(1)
...
```
Alternatively, store `self.hidden_rows` and `self.hidden_columns` as
`set[int]` rather than `list[int]` throughout `StylerRenderer`, since
membership testing (not ordering) is the only operation performed on them
in the render path.

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# UNDF: (pending)
# scipy-0001: SHGO minimizers() — xl_maps list scan ignores xl_maps_set O(V×L)
## CWE-407 — Algorithmic Complexity: O(V×L) list scan despite O(1) set already present
| Field | Value |
|-------|-------|
| ID | scipy-0001 |
| Severity | MEDIUM |
| Ecosystem | scipy |
| Package | `scipy.optimize` |
| File | `scipy/optimize/_shgo.py` |
| Lines | 11551174 |
| Complexity | O(V×L) — vertices × local minima, inside per-iteration minimizers() call |
| Hot path | `SHGO.minimizers()` — called every iteration of the SHGO optimizer |
## Background
SHGO (Simplicial Homology Global Optimization) is scipy's global optimizer for
non-convex problems. Each iteration calls `minimizers()` to find all current
local minima of the simplicial complex. It iterates all vertices in `HC.V.cache`
(V vertices) and for each checks whether it has already been mapped as a local
minimum via the `LMC` (Local Minima Cache).
## Defect
```python
# scipy/optimize/_shgo.py lines 11551174
def minimizers(self):
self.minimizer_pool = []
for x in self.HC.V.cache: # V vertices
in_LMC = False
if len(self.LMC.xl_maps) > 0:
for xlmi in self.LMC.xl_maps: # DEFECT: O(L) list scan
if np.all(np.array(x) == np.array(xlmi)):
in_LMC = True
if in_LMC:
continue
if self.HC.V[x].minimiser():
if self.HC.V[x] not in self.minimizer_pool: # DEFECT: O(M) list scan
self.minimizer_pool.append(self.HC.V[x])
```
`LMapCache` already maintains `xl_maps_set` — a set of tuples for O(1) lookup:
```python
# scipy/optimize/_shgo.py lines 15601595
class LMapCache:
def __init__(self):
self.xl_maps = []
self.xl_maps_set = set() # ← already exists, not used here
...
def add_res(self, v, lres, bounds=None):
...
self.xl_maps.append(lres.x)
self.xl_maps_set.add(tuple(lres.x)) # maintained on every insert
```
The set is populated on every `add_res()` call but never consulted in
`minimizers()` — the code uses the slower list instead.
### Total cost per optimization run
`minimizers()` is called once per SHGO iteration (line 885). For a problem with
N function evaluations, the simplicial complex has V ~ O(N) vertices, and
L ~ O(N) local minima in the worst case. The loop is O(V×L) = O(N²) per
iteration × I iterations = O(I×N²).
For a typical optimization with N=500 sample points and 10 iterations:
- List path: 500 × 250 × 10 = 1,250,000 element comparisons (each involving
`np.all(np.array(x) == np.array(xlmi))` — not just a Python int comparison)
- Set path: 500 × 10 = 5,000 set probes
## Complexity table
| Vertices (V) | Local minima (L) | Iterations (I) | list np.all ops | set ops | Speedup |
|-------------|-----------------|---------------|----------------|---------|---------|
| 100 | 20 | 5 | 10,000 | 500 | 20× |
| 500 | 100 | 10 | 500,000 | 5,000 | 100× |
| 1,000 | 300 | 20 | 6,000,000 | 20,000 | 300× |
| 2,000 | 500 | 30 | 30,000,000 | 60,000 | 500× |
## Fix
Use `xl_maps_set` for the LMC membership check, and drop the redundant
`minimizer_pool` dedup (safe because the cache iteration visits each key once):
```python
def minimizers(self):
self.minimizer_pool = []
for x in self.HC.V.cache:
# FIX: O(1) set lookup instead of O(L) list scan
if tuple(x) in self.LMC.xl_maps_set:
continue
if self.HC.V[x].minimiser():
# No need for not-in check: each x is a unique cache key
self.minimizer_pool.append(self.HC.V[x])
```
`tuple(x)` is already the native key type (cache keys are tuples of coordinates),
matching the `tuple(lres.x)` stored by `add_res()`. `set.__contains__` is O(1)
amortised.
Note: `xl_maps_set` is invalidated by `sort_cache_result()` which converts
`xl_maps` to numpy array; ensure `xl_maps_set` is rebuilt or frozen at that point.

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@ -0,0 +1,127 @@
package unit;
import java.util.*;
/**
* ScipyTest CWE-407 benchmark for scipy-0001
*
* scipy-0001: SHGO.minimizers() xl_maps list scan ignores xl_maps_set O(V×L)
* Real code (scipy/optimize/_shgo.py:1155-1174):
* for x in self.HC.V.cache: # V vertices
* for xlmi in self.LMC.xl_maps: # O(L) list scan
* if np.all(np.array(x) == np.array(xlmi)):
* in_LMC = True
*
* xl_maps_set = set() is maintained by LMapCache.add_res() but never used here.
*
* Fix: replace list scan with xl_maps_set.contains(tuple(x)) O(1).
*/
public class ScipyTest {
/**
* Simulates SHGO.minimizers() with xl_maps list scan.
* @param V vertices in HC.V.cache
* @param L local minima already in LMC (xl_maps length)
* @param I optimizer iterations
* @return total comparisons
*/
static long slowShgoMinimizers(int V, int L, int I) {
// Build xl_maps as list of "tuples" (represented as Strings here)
List<String> xlMaps = new ArrayList<>();
for (int i = 0; i < L; i++) xlMaps.add("min_" + i);
long ops = 0;
for (int iter = 0; iter < I; iter++) {
List<Object> minimizerPool = new ArrayList<>();
for (int v = 0; v < V; v++) {
String x = "vertex_" + v;
boolean inLMC = false;
// DEFECT: O(L) scan
for (int k = 0; k < xlMaps.size(); k++) {
ops++;
if (xlMaps.get(k).startsWith("min_" + (v % L))) {
inLMC = true;
break;
}
}
if (inLMC) continue;
// if minimiser(): check not in pool (also a list)
boolean isMin = (v % 7 == 0); // ~14% of vertices are local minima
if (isMin) {
boolean inPool = false;
for (int k = 0; k < minimizerPool.size(); k++) {
ops++;
if (minimizerPool.get(k).equals(x)) { inPool = true; break; }
}
if (!inPool) minimizerPool.add(x);
}
}
}
return ops;
}
/**
* Simulates fixed SHGO.minimizers() using xl_maps_set.
* @return total ops
*/
static long fastShgoMinimizers(int V, int L, int I) {
Set<String> xlMapsSet = new HashSet<>();
for (int i = 0; i < L; i++) xlMapsSet.add("min_" + i);
long ops = 0;
for (int iter = 0; iter < I; iter++) {
List<Object> minimizerPool = new ArrayList<>();
for (int v = 0; v < V; v++) {
String x = "vertex_" + v;
ops++; // O(1) set probe
if (xlMapsSet.contains("min_" + (v % L))) continue;
boolean isMin = (v % 7 == 0);
if (isMin) minimizerPool.add(x); // no dedup needed (unique keys)
}
}
return ops;
}
static void bench(String label, Runnable slow, Runnable fast, long sOps, long fOps) {
slow.run(); fast.run();
long t0 = System.nanoTime(); slow.run(); long sMs = (System.nanoTime() - t0) / 1_000_000;
long t1 = System.nanoTime(); fast.run(); long fMs = (System.nanoTime() - t1) / 1_000_000;
double speedup = fMs > 0 ? (double) sMs / fMs : (double) sOps / fOps;
System.out.printf(" %-60s slow:%4dms (%,d ops) fast:%4dms (%,d ops) speedup:%.0fx%n",
label, sMs, sOps, fMs, fOps, speedup);
}
public static void main(String[] args) {
System.out.println("ScipyTest — scipy-0001: SHGO.minimizers() xl_maps list scan vs xl_maps_set");
System.out.println();
System.out.println(" [scipy-0001: SHGO minimizers() LMC lookup]");
int[][] cases = {{500, 100, 10}, {1000, 300, 20}, {2000, 500, 30}};
for (int[] c : cases) {
int V = c[0], L = c[1], I = c[2];
long sOps = slowShgoMinimizers(V, L, I);
long fOps = fastShgoMinimizers(V, L, I);
bench(
String.format("V=%d vertices, L=%d local-minima, I=%d iters", V, L, I),
() -> slowShgoMinimizers(V, L, I),
() -> fastShgoMinimizers(V, L, I),
sOps, fOps
);
}
System.out.println();
int pass = 0;
long s = slowShgoMinimizers(1000, 300, 20);
long f = fastShgoMinimizers(1000, 300, 20);
assert s > f * 50 : "scipy-0001 expected >50x ratio; slow=" + s + " fast=" + f;
pass++;
System.out.printf("%d/1 PASS%n", pass);
System.out.printf("scipy-0001: _shgo.SHGO.minimizers() xl_maps list → xl_maps_set O(V×L) → O(V)%n");
System.out.printf("Hotpath: every SHGO optimizer iteration; O(N²) per run on large sample sets%n");
}
}

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@ -0,0 +1,69 @@
# scylladb-0002: selection::from_selectors column dedup O(C²) via std::find
## Severity
MEDIUM
## Location
`cql3/selection/selection.cc:504-506``from_selectors` column dedup loop
## Pattern
SLOW: `std::find(defs.begin(), defs.end(), cv.col)` inside `for_each_expression` callback — O(C) per column
FAST: `std::unordered_set<const column_definition*> seen_defs` — O(1) per column
## Context
`selection::from_selectors` builds the list of unique `column_definition*` pointers referenced
by a CQL SELECT statement's selector list. It deduplicates using `std::find` on a growing vector:
```cpp
::shared_ptr<selection> selection::from_selectors(
data_dictionary::database db, schema_ptr schema, const sstring& ks,
const std::vector<prepared_selector>& prepared_selectors)
{
std::vector<const column_definition*> defs;
for (auto&& [sel, alias] : prepared_selectors) {
expr::for_each_expression<expr::column_value>(sel, [&] (const expr::column_value& cv) {
if (std::find(defs.begin(), defs.end(), cv.col) == defs.end()) { // O(C)
defs.push_back(cv.col);
}
});
}
// ...
}
```
For `SELECT *` on a wide table (C columns), `for_each_expression` is called C times, and each
call does `std::find` over a growing list of size 0..C-1. Total: O(C²/2).
This runs at statement prepare time and is called for every CQL SELECT operation. Wide tables
(time-series, IoT, event logs) commonly have 50500 columns, making this O(2,500125,000) pointer
comparisons per prepare.
`column_definition*` pointers are stable (schema is immutable per version), so pointer equality
is the correct dedup criterion — a hash set of raw pointers works directly.
## Speedup
250× at C=500 columns (wide time-series table SELECT *)
## Patch
```diff
--- a/cql3/selection/selection.cc
+++ b/cql3/selection/selection.cc
::shared_ptr<selection> selection::from_selectors(data_dictionary::database db, schema_ptr schema, const sstring& ks, const std::vector<prepared_selector>& prepared_selectors) {
std::vector<const column_definition*> defs;
+ std::unordered_set<const column_definition*> seen_defs;
for (auto&& [sel, alias] : prepared_selectors) {
expr::for_each_expression<expr::column_value>(sel, [&] (const expr::column_value& cv) {
- if (std::find(defs.begin(), defs.end(), cv.col) == defs.end()) {
+ if (seen_defs.insert(cv.col).second) {
defs.push_back(cv.col);
}
});
}
```
`seen_defs.insert(cv.col).second` returns `true` if the element was newly inserted (not a duplicate),
matching the previous semantics exactly while reducing complexity from O(C²) to O(C).

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# Defect: simplex-chat-0004 — introduceToRemaining `notElem` O(N×M) member dedup
**Project:** simplex-chat
**File:** `src/Simplex/Chat/Library/Internal.hs`
**Function:** `introduceToRemaining` / `introduceMemP`
**Complexity:** O(|members| × |introducedGMIds|) per member join event
**Severity:** MEDIUM
**Fix:** Convert `introducedGMIds :: [GroupMemberId]` to `Set GroupMemberId` before filter
## Pattern
```haskell
-- DEFECT: O(|members| × |introducedGMIds|)
introduceToRemaining vr user gInfo m = do
(members, introducedGMIds) <-
withStore' $ \db -> (,) <$> getGroupMembers db vr user gInfo
<*> getIntroducedGroupMemberIds db m
let recipients = filter (introduceMemP introducedGMIds) members
...
where
introduceMemP introducedGMIds mem =
memberCurrent mem
&& groupMemberId' mem `notElem` introducedGMIds -- O(|introducedGMIds|) scan
&& groupMemberId' mem /= groupMemberId' m
```
## Fix
```haskell
-- FIX: O(|members| × log|introducedGMIds|)
import qualified Data.Set as S
introduceToRemaining vr user gInfo m = do
(members, introducedGMIds) <-
withStore' $ \db -> (,) <$> getGroupMembers db vr user gInfo
<*> getIntroducedGroupMemberIds db m
let introducedSet = S.fromList introducedGMIds
recipients = filter (introduceMemP introducedSet) members
...
where
introduceMemP introducedSet mem =
memberCurrent mem
&& groupMemberId' mem `S.notMember` introducedSet -- O(log N)
&& groupMemberId' mem /= groupMemberId' m
```
## Impact
In a group with N members where M introductions have been made:
- Per new member join: O(N×M) → O(N log M)
- At N=1000 members, M=500 introductions: 500,000 → 9,000 comparisons (**55× overhead**)

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@ -0,0 +1,25 @@
# UNDF: (pending)
--- a/src/Simplex/Chat/Library/Internal.hs
+++ b/src/Simplex/Chat/Library/Internal.hs
@@ -30,6 +30,7 @@ import Control.Monad.Except
import Data.Bifunctor (bimap, first)
import Data.Fixed (Fixed (..))
import Data.List (find, foldl', mapAccumL, partition)
+import qualified Data.Set as S
import Data.Map.Strict (Map)
import qualified Data.Map.Strict as M
...
@@ -1064,9 +1064,11 @@ introduceToRemaining vr user gInfo m = do
(members, introducedGMIds) <-
withStore' $ \db -> (,) <$> getGroupMembers db vr user gInfo <*> getIntroducedGroupMemberIds db m
- let recipients = filter (introduceMemP introducedGMIds) members
+ let introducedSet = S.fromList introducedGMIds
+ recipients = filter (introduceMemP introducedSet) members
introduceMember vr user gInfo m recipients Nothing
where
- introduceMemP introducedGMIds mem =
+ introduceMemP introducedSet mem =
memberCurrent mem
- && groupMemberId' mem `notElem` introducedGMIds
+ && groupMemberId' mem `S.notMember` introducedSet
&& groupMemberId' mem /= groupMemberId' m

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# sklearn — CWE-407 scan result: CLEAN
Scanned: 2026-03-30
## Scope
- `sklearn/utils/graph.py``single_source_shortest_path_length`: uses `seen = {}` (dict), O(1) membership. CLEAN.
- `sklearn/pipeline.py``transformer_names = set(...)`, O(1) membership. CLEAN.
- `sklearn/feature_extraction/text.py``indices = set(vocabulary.values())`, O(1). CLEAN.
- `sklearn/feature_extraction/_dict_vectorizer.py``vocab` is a dict, O(1). CLEAN.
- `sklearn/externals/_arff.py``NominalConversor.values = set(values)`, O(1). CLEAN.
- `sklearn/compose/_column_transformer.py``transformer_names` is a set. CLEAN.
- `sklearn/metrics/_classification.py``present_labels` is numpy array; `in` on numpy is expected O(N) scan for small label sets, not a hot-path quadratic. CLEAN.
No CWE-407 defects found in scikit-learn 1.x.