一开始以为是最小流，最后却是堆优化dijkstra

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

const int N = 100000,INF = 0x3f3f3f3f;

int to[N],ne[N],w[N],dist[N],head[N],tot,n,m,st1,ed;
bool st[N];

void add(int u,int v,int c)
{
	to[tot] = v;w[tot] = c;ne[tot] = head[u];head[u] = tot++;
}

int dijkstra()
{
	memset(dist,INF,sizeof dist);
	priority_queue<pair<int,int> > heap;
	dist[st1] = 0;
	heap.push({0,st1});
	while(heap.size())
	{
		int t = heap.top().second;heap.pop();
		if(st[t]) continue;
		for(int i=head[t];i!=-1;i = ne[i])
		{
			int j = to[i],k = w[i];
			if(dist[j]>dist[t]+k)
			{
				dist[j] = dist[t]+k;
				heap.push({-dist[j],j});
			}
		}
	}
	if(dist[ed] == INF) return -1;
	else return dist[ed];
}

int main()
{
	cin >> n >> m >> st1 >> ed;
	memset(head,-1,sizeof head);
	for(int i=0;i<m;i++)
	{
		int a,b,c;
		cin >> a >> b >> c;
		add(a,b,c);
		add(b,a,c);
	}
	int ans = dijkstra();
	cout << ans;
	return 0;
}