python/TangDou/AcWing/P1339_SPFA.cpp

#include <bits/stdc++.h>

using namespace std;
const int INF = 0x3f3f3f3f;
const int N = 2510;          //结点数
const int M = 6200 * 2 + 10; //边数

int n, m; // n个结点，m条边
int s, t; //起点，终点

//邻接表
int h[N], e[M], w[M], ne[M], idx;
void add(int a, int b, int c) {
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}
int d[N];   //最短距离数组
bool st[N]; //是不是进过队列

// spfa模板
void spfa(int start) {
    //将所有距离初始化为无穷大
    memset(d, 0x3f, sizeof d);

    //出发点的距离清零
    d[start] = 0;
    queue<int> q;
    q.push(start);    //出发点入队列
    st[start] = true; //出发点标识已使用

    while (q.size()) {
        int t = q.front();
        q.pop();
        st[t] = false;
        for (int i = h[t]; ~i; i = ne[i]) {
            int j = e[i];
            if (d[j] > d[t] + w[i]) {
                d[j] = d[t] + w[i];
                if (!st[j]) {
                    st[j] = true;
                    q.push(j);
                }
            }
        }
    }
}

int main() {
    memset(h, -1, sizeof h);
    cin >> n >> m >> s >> t;
    for (int i = 0; i < m; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c), add(b, a, c);
    }
    spfa(s);
    cout << d[t] << endl;
    return 0;
}