acwing851. spfa求最短路

#include<iostream>
#include<cstring>
#include<queue>
using namespace std;

const int N=1e5+10;

int ne[N],e[N],h[N],idx,w[N];
int n,m,dist[N];
bool st[N];

void add(int a,int b,int c){
    e[idx]=b;
    w[idx]=c;
    ne[idx]=h[a];
    h[a]=idx++;
}
int spfa(){
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    queue<int> q;
    q.push(1);
    st[1]=true;
    while(q.size()){
        int t=q.front();
        q.pop();
        st[t]=false;
        for(int i=h[t];i!=-1;i=ne[i]){
            int j=e[i];
            if(dist[j]>dist[t]+w[i]){
                dist[j]=dist[t]+w[i];
                if(!st[j]){
                    q.push(j);
                    st[j]=true;
                }
            }
        }
    }
    return dist[n];
}
int main(){
    cin>>n>>m;
    int a,b,c;
    memset(h,-1,sizeof h);
    while(m--){
        cin>>a>>b>>c;
        add(a,b,c);
    }
    int res=spfa();
    if(res!=0x3f3f3f3f)cout<<res<<endl;
    else cout<<"impossible"<<endl;
    return 0;
}