【算法代码】

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

typedef pair<int,int> PII; //<dis,idx>
const int inf=0x3f3f3f3f;
const int N=5e2+5,M=1e5+5;
int h[N],e[M],ne[M],val[M],idx;
int st[N],dis[N];
int n,m;

void add(int a,int b,int w) {
    val[idx]=w,e[idx]=b,ne[idx]=h[a],h[a]=idx++;
}

int dijkstra() {
    priority_queue<PII,vector<PII>,greater<PII>> q;
    memset(dis,inf,sizeof dis);
    dis[1]=0;
    q.push({0,1}); //<dis,idx>

    while(!q.empty()) {
        auto t=q.top();
        q.pop();
        int u=t.second; //idx
        if(st[u]) continue;
        st[u]=true;
        for(int i=h[u]; i!=-1; i=ne[i]) {
            int j=e[i];
            if(dis[j]>dis[u]+val[i]) {
                dis[j]=dis[u]+val[i];
                q.push({dis[j],j});
            }
        }
    }

    if(dis[n]==inf) return -1;
    return dis[n];
}

int main() {
    memset(h,-1,sizeof(h));
    cin>>n>>m;
    while(m--) {
        int a,b,c;
        cin>>a>>b>>c;
        add(a,b,c);
    }
    cout<<dijkstra()<<endl;

    return 0;
}

/*
in:
3 3
1 2 2
2 3 1
1 3 4

out:
3
*/