先从n号点开始跑dij,然后将从每一个点出发的边按到达的点到n号点的距离排序，然后dfs剪枝

跑得很快，每个点不到10ms，但是WA on #4

这是为什么？

#include<bits/stdc++.h>
using namespace std;
const int N=210,M=10010;
int x[N],y[N];
int n,m;
vector<pair<int,int> >g[N];
double dis[N][N];
double dist[N];
bool st[N];
bool vis[M];
typedef pair<double,int>node;
void dij(){
	priority_queue<node,vector<node>,greater<node> >q;
	q.push({0,n});
	memset(dist,0x7f,sizeof dist);
	dist[n]=0;
	while(q.size()){
		int t=q.top().second;q.pop();
		if(st[t])	continue;
		st[t]=1;
		for(int i=0;i<g[t].size();i++){
			int j=g[t][i].first;
			if(st[j])	continue;
			if(dist[j]>dist[t]+dis[t][j]){
				dist[j]=dist[t]+dis[t][j];
				q.push({dist[j],j});
			}
		}
	}
}
bool cmp(pair<int,int>a,pair<int,int>b){
	return dist[a.first]<dist[b.first];
}
double small=1e100,small2=1e100;
void dfs(int u,double len){
	if(len+dist[u]>=small2)	return;
	//printf("%d %lf %d\n",u,len,loop);
	if(u==n){
		if(len<small){
			small2=small,small=len;
		}
		else{
			if(len<small2){
				small2=len;
			}
		}
	}
	for(auto v:g[u]){
		if(vis[v.second])	continue;
		vis[v.second]=1;
		dfs(v.first,len+dis[v.first][u]);
		vis[v.second]=0;
		if(len>=small2)	return;
	}
}
int main(){
	//freopen("b.in","r",stdin);
	//freopen("b.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)	scanf("%d%d",&x[i],&y[i]);
	for(int i=1;i<=m;i++){
		int a,b;scanf("%d%d",&a,&b);
		g[a].push_back({b,i});
		g[b].push_back({a,i});
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			dis[i][j]=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
		}
	}
	dij();
	if(dist[1]==1e100){
		puts("-1");
		return 0;
	}
	for(int i=1;i<=n;i++)	sort(g[i].begin(),g[i].end(),cmp);
	dfs(1,0);
	if(small2==1e100){
		puts("-1");
	}
	else{
		printf("%.2lf\n",small2);
	}
	return 0;
}