spfa 最短路

#include <bits/stdc++.h>
using namespace std;

#define pb push_back
#define INF 1e16;
typedef long long ll;
typedef pair<int,ll> pil;
const int N = 1e3+10;

int n,m,st,ed;
ll mp[N][N];
bool vis[N]; ll dis[N];

int main ()
{
    freopen("in.txt", "r", stdin);
    memset(mp, 
 
0x3f, sizeof(mp));
    scanf("%d %d %d %d", &n, &m, &st, &ed);
    for(int i=1; i<=m; i++) {
        int u,v; ll w; 
        scanf("%d %d %lld", &u, &v, &w);
        mp[u][v]=min(mp[u][v], w);
        mp[v][u]=mp[u][v];
    }
    for(int i=0; i<=n; i++) {
        dis[i] 
 
= INF; vis[i] = false;
    }
        
    dis[st] = 0;
    queue<int> que;
    que.push(st);
    vis[st] = true;
    while(!que.empty()) {
        // pil ans = que.front(); que.pop();
        // int tmp = ans.first;
        // ll L = ans.second; 
        int tmp = que.front(); que.pop();
        vis[tmp] 
 
= 0;
        for(int i=1; i<=n; i++) {
            // int v = mp[tmp][i].first;
            if(tmp == i) continue;
            ll dd = mp[tmp][i];
            if(dis[tmp] + dd < dis[i]) {
                dis[i] = dis[tmp] + dd;
                if(!vis[i]) {
                    vis[i] = true;
                    que.push(i);
                }
            }
        }
    }
    printf("%lld\n", dis[ed]);
    return 0;
}