java-topology/defects/openxcom-0001/test/test_reachable_lookup.cpp

// Unit test for openxcom-0001: AIModule _reachable/_reachableWithAttack
// vector std::find O(N*R) -> unordered_set O(1) lookup
//
// Defect: AIModule stores reachable tile indices in std::vector<int> and
// uses std::find() for membership checks inside loops over map nodes
// (setupAmbush, setupEscape, selectPointNearTarget, findFirePoint).
// On a 50x50x4 map with hundreds of reachable tiles, each AI turn
// performs O(N*R) linear scans where N = nodes checked and R = reachable tiles.
//
// Fix: Replace std::vector<int> with std::unordered_set<int> for O(1) lookup.

#include <vector>
#include <unordered_set>
#include <algorithm>
#include <chrono>
#include <iostream>
#include <cassert>
#include <cstdlib>

// Simulate our defective pattern: vector + std::find in loop
int benchmarkVector(const std::vector<int>& reachable, const std::vector<int>& queries) {
    int found = 0;
    for (size_t i = 0; i < queries.size(); ++i) {
        if (std::find(reachable.begin(), reachable.end(), queries[i]) != reachable.end()) {
            ++found;
        }
    }
    return found;
}

// Simulate our fixed pattern: unordered_set + count in loop
int benchmarkSet(const std::unordered_set<int>& reachable, const std::vector<int>& queries) {
    int found = 0;
    for (size_t i = 0; i < queries.size(); ++i) {
        if (reachable.count(queries[i]) != 0) {
            ++found;
        }
    }
    return found;
}

int main() {
    // Typical battlescape: 50x50x4 = 10000 tiles, ~500 reachable
    const int R = 500;   // reachable tiles
    const int N = 200;   // nodes/positions checked per AI cycle (setupAmbush + findFirePoint + selectPointNearTarget)
    const int UNITS = 20; // alien units per battle
    const int ITERATIONS = UNITS; // each unit runs AI per turn

    // Build reachable tile indices
    std::vector<int> reachableVec;
    reachableVec.reserve(R);
    for (int i = 0; i < R; ++i) {
        reachableVec.push_back(i * 20); // spread across map
    }
    std::unordered_set<int> reachableSet(reachableVec.begin(), reachableVec.end());

    // Build query positions (mix of reachable and unreachable)
    std::vector<int> queries;
    queries.reserve(N);
    for (int i = 0; i < N; ++i) {
        queries.push_back(i * 10); // ~50% will hit
    }

    // Correctness check
    int vecResult = benchmarkVector(reachableVec, queries);
    int setResult = benchmarkSet(reachableSet, queries);
    assert(vecResult == setResult);
    std::cout << "Correctness: PASS (both found " << vecResult << " matches)" << std::endl;

    // Benchmark: vector (defective)
    auto t0 = std::chrono::high_resolution_clock::now();
    int dummy1 = 0;
    for (int iter = 0; iter < ITERATIONS; ++iter) {
        dummy1 += benchmarkVector(reachableVec, queries);
    }
    auto t1 = std::chrono::high_resolution_clock::now();

    // Benchmark: unordered_set (fixed)
    auto t2 = std::chrono::high_resolution_clock::now();
    int dummy2 = 0;
    for (int iter = 0; iter < ITERATIONS; ++iter) {
        dummy2 += benchmarkSet(reachableSet, queries);
    }
    auto t3 = std::chrono::high_resolution_clock::now();

    double vecUs = std::chrono::duration_cast<std::chrono::microseconds>(t1 - t0).count();
    double setUs = std::chrono::duration_cast<std::chrono::microseconds>(t3 - t2).count();

    double ratio = vecUs / (setUs > 0 ? setUs : 1);

    std::cout << "Vector (defective): " << vecUs << " us" << std::endl;
    std::cout << "Set    (fixed):     " << setUs << " us" << std::endl;
    std::cout << "Ratio: " << ratio << "x" << std::endl;
    std::cout << "Parameters: R=" << R << " tiles reachable, N=" << N << " queries, "
              << UNITS << " units per turn" << std::endl;

    // Verify significant speedup
    assert(ratio > 2.0);
    std::cout << "Performance: PASS (ratio > 2x)" << std::endl;

    // Prevent optimizer from removing work
    assert(dummy1 == dummy2);

    std::cout << "ALL TESTS PASSED" << std::endl;
    return 0;
}