228 lines
9.1 KiB
Java
228 lines
9.1 KiB
Java
package unit;
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import java.util.*;
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/**
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* Unit test for valhalla-0001:
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* linkclassification.cc — IsSlipLane() nested linear scan O(F×R).
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*
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* Simulates the intersection-check loop:
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* for (node : reverse_nodes) // R iterations
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* std::find(forward_nodes.begin(), ..., node) // O(F) linear scan
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*
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* vs. the fixed version using unordered_set:
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* forward_set = unordered_set(forward_nodes)
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* for (node : reverse_nodes) // R iterations
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* forward_set.count(node) // O(1) hash lookup
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*
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* Compile: javac -d . IsSlipLaneAlgorithm.java
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* Run: java -ea unit.IsSlipLaneAlgorithm
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*/
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public class IsSlipLaneAlgorithm {
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static int checkCount = 0;
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static int passCount = 0;
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static void check(String desc, boolean cond) {
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checkCount++;
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if (!cond) {
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System.out.println("FAIL [" + checkCount + "]: " + desc);
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} else {
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passCount++;
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System.out.println("PASS [" + checkCount + "]: " + desc);
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}
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}
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// -------------------------------------------------------------------------
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// Slow path: std::find linear scan over forward_nodes for each reverse node
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// -------------------------------------------------------------------------
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static class SlowIntersectionFinder {
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int ops = 0;
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boolean find(int[] forwardNodes, int target) {
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for (int n : forwardNodes) {
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ops++;
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if (n == target) return true;
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}
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return false;
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}
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/** Returns intersection node index, or -1 if none */
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int findIntersection(int[] forwardNodes, int[] reverseNodes) {
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for (int node : reverseNodes) {
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if (find(forwardNodes, node)) {
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return node;
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}
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}
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return -1;
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}
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}
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// -------------------------------------------------------------------------
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// Fast path: unordered_set (HashSet) O(1) lookup
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// -------------------------------------------------------------------------
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static class FastIntersectionFinder {
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int ops = 0;
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int findIntersection(int[] forwardNodes, int[] reverseNodes) {
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// Build set from forward_nodes once — O(F)
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Set<Integer> forwardSet = new HashSet<>(forwardNodes.length * 2);
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for (int n : forwardNodes) forwardSet.add(n);
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for (int node : reverseNodes) {
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ops++;
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if (forwardSet.contains(node)) {
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return node;
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}
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}
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return -1;
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}
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}
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// -------------------------------------------------------------------------
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// Build test data: two vectors of node IDs that share a suffix
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// forward_nodes: 0, 1, 2, ..., F-1
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// reverse_nodes: F*2, F*2+1, ..., F*2+R-sharedSuffix-1, then F-sharedSuffix, ..., F-1
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// Intersection is at node F-sharedSuffix (last shared node in forward, first in overlap)
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// If sharedSuffix == 0, no intersection exists (worst-case: scan all R × F)
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// -------------------------------------------------------------------------
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static int[] buildForwardNodes(int F) {
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int[] nodes = new int[F];
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for (int i = 0; i < F; i++) nodes[i] = i;
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return nodes;
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}
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static int[] buildReverseNodes(int F, int R, int sharedSuffix) {
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// First (R - sharedSuffix) nodes are unique to reverse, rest overlap with forward tail
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int[] nodes = new int[R];
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int uniqueCount = R - sharedSuffix;
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for (int i = 0; i < uniqueCount; i++) {
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nodes[i] = F * 2 + i; // disjoint from forward
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}
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for (int i = 0; i < sharedSuffix; i++) {
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nodes[uniqueCount + i] = F - sharedSuffix + i; // overlaps with forward tail
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}
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return nodes;
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}
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public static void main(String[] args) {
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System.out.println("=== valhalla-0001: IsSlipLane forward_nodes linear scan ===\n");
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// --- Test 1: correctness — both paths find the same intersection ---
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{
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int F = 20, R = 20, shared = 5;
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int[] fwd = buildForwardNodes(F);
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int[] rev = buildReverseNodes(F, R, shared);
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SlowIntersectionFinder slow = new SlowIntersectionFinder();
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FastIntersectionFinder fast = new FastIntersectionFinder();
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int slowResult = slow.findIntersection(fwd, rev);
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int fastResult = fast.findIntersection(fwd, rev);
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check("correctness: intersection found by both paths",
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slowResult != -1 && fastResult != -1);
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check("correctness: both agree on intersection node ("
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+ slowResult + " == " + fastResult + ")", slowResult == fastResult);
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}
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// --- Test 2: correctness — no intersection case ---
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{
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int F = 20, R = 20, shared = 0;
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int[] fwd = buildForwardNodes(F);
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int[] rev = buildReverseNodes(F, R, shared);
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SlowIntersectionFinder slow = new SlowIntersectionFinder();
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FastIntersectionFinder fast = new FastIntersectionFinder();
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int slowResult = slow.findIntersection(fwd, rev);
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int fastResult = fast.findIntersection(fwd, rev);
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check("no-intersection: both return -1 (slow=" + slowResult + " fast=" + fastResult + ")",
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slowResult == -1 && fastResult == -1);
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}
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// --- Test 3: complexity — worst case (no intersection) ---
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{
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// No shared nodes → slow does F×R comparisons
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int F = 200, R = 200;
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int[] fwd = buildForwardNodes(F);
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int[] rev = buildReverseNodes(F, R, 0); // no intersection
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SlowIntersectionFinder slow = new SlowIntersectionFinder();
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FastIntersectionFinder fast = new FastIntersectionFinder();
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slow.findIntersection(fwd, rev);
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fast.findIntersection(fwd, rev);
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long expectedSlowOps = (long) F * R; // scans all F for each of R reverse nodes
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double ratio = (double) slow.ops / fast.ops;
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check("worst-case: slow_ops == F*R ("
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+ slow.ops + " == " + expectedSlowOps + ")", slow.ops == expectedSlowOps);
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check("worst-case: fast_ops == R ("
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+ fast.ops + " == " + R + ")", fast.ops == R);
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check("worst-case: ratio >= 10x (actual " + String.format("%.1f", ratio) + "x)",
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ratio >= 10.0);
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System.out.println(" slow_ops=" + slow.ops + " fast_ops=" + fast.ops
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+ " ratio=" + String.format("%.0f", ratio) + "x (F=" + F + " R=" + R + ")");
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}
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// --- Test 4: complexity — early exit (intersection at start of reverse) ---
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{
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// Intersection at first reverse node → slow does F comparisons, fast does 1
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int F = 200, R = 200;
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int[] fwd = buildForwardNodes(F);
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// Make first reverse node = 0 (first forward node → found immediately in fast,
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// but slow scans forward until it finds it = position 0 = 1 op)
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int[] rev = new int[R];
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rev[0] = 0; // immediately in forward set
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for (int i = 1; i < R; i++) rev[i] = F * 2 + i; // rest disjoint
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SlowIntersectionFinder slow = new SlowIntersectionFinder();
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FastIntersectionFinder fast = new FastIntersectionFinder();
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int slowResult = slow.findIntersection(fwd, rev);
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int fastResult = fast.findIntersection(fwd, rev);
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check("early-exit: both find node 0", slowResult == 0 && fastResult == 0);
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check("early-exit: slow_ops=1 (found at start of forward)",
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slow.ops == 1);
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check("early-exit: fast_ops=1 (hash lookup)", fast.ops == 1);
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}
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// --- Test 5: complexity — intersection at END of forward (worst linear scan) ---
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{
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// Intersection at forward[F-1] → slow must scan all F nodes before finding match
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int F = 300, R = 100;
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int[] fwd = buildForwardNodes(F);
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// rev[0] = F-1 → found, but only after scanning all F forward nodes (slow)
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int[] rev = new int[R];
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rev[0] = F - 1;
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for (int i = 1; i < R; i++) rev[i] = F * 2 + i;
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SlowIntersectionFinder slow = new SlowIntersectionFinder();
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FastIntersectionFinder fast = new FastIntersectionFinder();
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slow.findIntersection(fwd, rev);
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fast.findIntersection(fwd, rev);
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double ratio = (double) slow.ops / fast.ops;
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check("tail-match: slow_ops == F (scanned all forward, slow=" + slow.ops + ")",
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slow.ops == F);
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check("tail-match: fast_ops == 1 (hash, fast=" + fast.ops + ")", fast.ops == 1);
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check("tail-match: ratio >= F (" + String.format("%.0f", ratio) + "x >= " + F + "x)",
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ratio >= F);
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System.out.println(" slow_ops=" + slow.ops + " fast_ops=" + fast.ops
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+ " ratio=" + String.format("%.0f", ratio) + "x (F=" + F + " R=" + R + ")");
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}
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System.out.println("\n" + passCount + "/" + checkCount + " PASS");
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}
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}
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