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2 years ago
#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
typedef pair<int, int> PII;
//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
//迪杰斯特拉
void dijkstra(int start) {
memset(d, 0x3f, sizeof d); //初始化距离为无穷大
memset(st, 0, sizeof st); //初始化为未出队列过
d[start] = 0; //出发点距离0
priority_queue<PII, vector<PII>, greater<PII>> q; //小顶堆
q.push({0, start}); //出发点入队列
while (q.size()) {
auto t = q.top();
q.pop();
int u = t.second;
if (st[u]) continue;
st[u] = true;
for (int i = h[u]; ~i; i = ne[i]) {
int j = e[i];
if (d[j] > d[u] + w[i]) {
d[j] = d[u] + w[i];
q.push({d[j], 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);
}
dijkstra(s);
cout << d[t] << endl;
return 0;
}