java-topology/defects/vim/unit/InsComplDedupTest.java

package unit;

import java.util.*;

/**
 * vim-0001: ins_compl_add linked-list linear scan O(N²) in insert-mode completion.
 *
 * Models ins_compl_add_matches() calling ins_compl_add() for N candidates.
 * Each ins_compl_add() does a full O(M) walk of the existing completions linked
 * list to check for duplicates. Total work is O(N²).
 *
 * The fix replaces the linked-list scan with a HashSet lookup: O(N) total.
 */
public class InsComplDedupTest {

    // ----- SLOW path: linked-list dedup (mirrors Vim's insexpand.c) -----

    static class ComplNode {
        String str;
        ComplNode next;
        ComplNode(String s) { this.str = s; }
    }

    /** Returns op count for adding one candidate to the linked list. */
    static long slowAddCandidate(ComplNode head, String candidate, long[] ops) {
        // Walk linked list to check for duplicates — O(M)
        ComplNode cur = head;
        while (cur != null) {
            ops[0]++;
            if (cur.str.equals(candidate)) {
                return -1; // already present
            }
            cur = cur.next;
        }
        return 0; // not found — would be added
    }

    static long slowBuildCompletions(String[] candidates) {
        long[] ops = {0};
        ComplNode head = null;
        ComplNode tail = null;
        List<String> accepted = new ArrayList<>();

        for (String c : candidates) {
            // Simulate the head-pointer (compl_first_match is not null)
            if (head == null) {
                head = new ComplNode(c);
                tail = head;
                accepted.add(c);
                continue;
            }
            long result = slowAddCandidate(head, c, ops);
            if (result == 0) {
                // Add to list
                ComplNode node = new ComplNode(c);
                tail.next = node;
                tail = node;
                accepted.add(c);
            }
        }
        return ops[0];
    }

    // ----- FAST path: HashSet dedup -----

    static long fastBuildCompletions(String[] candidates) {
        long ops = 0;
        Set<String> seen = new HashSet<>();
        for (String c : candidates) {
            ops++;  // O(1) hash lookup
            seen.add(c);
        }
        return ops;
    }

    // ----- Test runner -----

    public static void main(String[] args) {
        System.out.println("vim-0001: InsComplDedupTest");
        System.out.println("==========================");

        int passed = 0;
        int total = 0;

        // Test 1: correctness — both paths accept same unique elements
        {
            total++;
            String[] cands = {"alpha", "beta", "gamma", "alpha", "delta", "beta"};
            // Slow path: collect accepted list
            long[] ops = {0};
            ComplNode head = null;
            ComplNode tail = null;
            List<String> slowAccepted = new ArrayList<>();
            for (String c : cands) {
                if (head == null) {
                    head = new ComplNode(c); tail = head;
                    slowAccepted.add(c); continue;
                }
                if (slowAddCandidate(head, c, ops) == 0) {
                    ComplNode node = new ComplNode(c); tail.next = node; tail = node;
                    slowAccepted.add(c);
                }
            }
            Set<String> fastAccepted = new HashSet<>(Arrays.asList(cands));
            boolean ok = new HashSet<>(slowAccepted).equals(fastAccepted);
            System.out.println("Test 1 (correctness): " + (ok ? "PASS" : "FAIL"));
            if (ok) passed++;
        }

        // Test 2: op-count ratio >= 5x at N=200 unique candidates
        {
            total++;
            int N = 200;
            String[] candidates = new String[N];
            for (int i = 0; i < N; i++) candidates[i] = "word_" + i;

            long slowOps = slowBuildCompletions(candidates);
            long fastOps = fastBuildCompletions(candidates);
            double ratio = (double) slowOps / fastOps;

            System.out.printf("Test 2 (N=%d unique): slow=%d ops, fast=%d ops, ratio=%.1fx%n",
                    N, slowOps, fastOps, ratio);
            boolean ok = ratio >= 5.0;
            System.out.println("Test 2 (ratio >= 5x): " + (ok ? "PASS" : "FAIL"));
            if (ok) passed++;
        }

        // Test 3: op-count ratio >= 50x at N=500 unique candidates
        {
            total++;
            int N = 500;
            String[] candidates = new String[N];
            for (int i = 0; i < N; i++) candidates[i] = "word_" + i;

            long slowOps = slowBuildCompletions(candidates);
            long fastOps = fastBuildCompletions(candidates);
            double ratio = (double) slowOps / fastOps;

            System.out.printf("Test 3 (N=%d unique): slow=%d ops, fast=%d ops, ratio=%.1fx%n",
                    N, slowOps, fastOps, ratio);
            boolean ok = ratio >= 50.0;
            System.out.println("Test 3 (ratio >= 50x): " + (ok ? "PASS" : "FAIL"));
            if (ok) passed++;
        }

        // Test 4: op-count ratio >= 100x at N=1000 unique candidates
        {
            total++;
            int N = 1000;
            String[] candidates = new String[N];
            for (int i = 0; i < N; i++) candidates[i] = "word_" + i;

            long slowOps = slowBuildCompletions(candidates);
            long fastOps = fastBuildCompletions(candidates);
            double ratio = (double) slowOps / fastOps;

            System.out.printf("Test 4 (N=%d unique): slow=%d ops, fast=%d ops, ratio=%.1fx%n",
                    N, slowOps, fastOps, ratio);
            boolean ok = ratio >= 100.0;
            System.out.println("Test 4 (ratio >= 100x): " + (ok ? "PASS" : "FAIL"));
            if (ok) passed++;
        }

        // Test 5: with duplicates — correctness and ratio hold
        {
            total++;
            int N = 400;
            String[] candidates = new String[N];
            for (int i = 0; i < N; i++) candidates[i] = "dup_" + (i % 50); // 50 unique, 8 dups each

            long slowOps = slowBuildCompletions(candidates);
            long fastOps = fastBuildCompletions(candidates);
            double ratio = (double) slowOps / fastOps;

            System.out.printf("Test 5 (N=%d w/dups, 50 unique): slow=%d ops, fast=%d ops, ratio=%.1fx%n",
                    N, slowOps, fastOps, ratio);
            boolean ok = ratio >= 5.0;
            System.out.println("Test 5 (ratio >= 5x): " + (ok ? "PASS" : "FAIL"));
            if (ok) passed++;
        }

        System.out.println();
        System.out.println(passed + "/" + total + " PASS");
        assert passed == total : passed + "/" + total + " tests passed";
    }
}