spfa求最短路

题目:

题解:

spfa模板

#include <bits/stdc++.h>
using namespace std;
const int N=1e5+10;
int w[N],e[N],ne[N],h[N],dis[N],vis[N],idx;
int n,m;
typedef pair<int,int> pll;
int inf=0x3f3f3f3f;
void add(int a,int b,int c)
{
    w[idx]=c;
    e[idx]=b;
    ne[idx]=h[a];
    h[a]=idx++;
}
void spfa()
{
    memset(dis,inf,sizeof(dis));
    dis[1]=0;
    queue<pll> q;
    q.push({0,1});
    vis[1]=1;
    while(q.size())
    {
        pll k=q.front();
        q.pop();
        int t=k.second;
        vis[t]=0;
        for(int i=h[t];i!=-1;i=ne[i])
        {
            int j=e[i];
            if(dis[j]>dis[t]+w[i])
            {
                dis[j]=dis[t]+w[i];
                if(!vis[j])
                {
                    vis[j]=1;
                    q.push({dis[j],j});
                }
            }
        }
    }
    if(dis[n]==inf) cout<<"impossible"<<endl;
    else cout<<dis[n]<<endl;
}
int main()
{
    cin>>n>>m;
    memset(h,-1,sizeof(h));
    while(m--)
    {
        int a,b,c;
        cin>>a>>b>>c;
        add(a,b,c);
    }
    spfa();
    return 0;
}