algo-aha

Floyd-Warshall算法，三重循环松弛

• https://leetcode.com/problems/network-delay-time/

int networkDelayTime(vector<vector<int>>& times, int N, int K) {
    // Floyd-Warshall算法，所有点对的最短路径
    const int INF = 1e7;
    vector<vector<int>> dist(N + 1, vector<int>(N + 1, INF));
    for (int i = 1; i <= N; i++) {
        dist[i][i] = 0;
    }
    for (auto &e : times) {
        dist[e[0]][e[1]] = e[2];
    }
    
    // 三重循环松弛
    for (int k = 1; k <= N; k++) {
        for (int i = 1; i <= N; i++) {
            for (int j = 1; j <= N; j++) {
                dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
            }
        }
    }

    int ans = INT_MIN;
    for (int i = 1; i <= N; i++) {
        ans = max(ans, dist[K][i]);
    }
    return (ans != INF) ? ans : -1;
}