最短路 SPFA 模板

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <queue>
#include <cstring>

using namespace std;
typedef long long ll;
#define MAX 1005
#define inf 0x3f3f3f3f
int dis[MAX],u[MAX],v[MAX],vis[MAX],next[MAX],c[MAX],w[MAX];
int first[10*MAX];//边的大小
void spfa(int vs,int n)
{
    queue<int> q;
    for(int i=1;i<=n;i++)
        dis[i] = inf;
    dis[vs] = 0;
    memset(vis,0,sizeof(vis));
    vis[vs] = 1;
    q.push(vs);
    int f = 0;
    while(!q.empty())
    {
        int x = q.front();
        q.pop();
        vis[x] = 0;
        for(int k=first[x];k!=-1;k=next[k])
        {
            if(dis[v[k]] > dis[x] + w[k])
            {
                dis[v[k]] = dis[x] + w[k];
                if(!vis[v[k]])
                {
                    vis[v[k]] = 1;
                    c[v[k]]++;
                    q.push(v[k]);
                    if(c[v[k]] > n)//入队次数超过上限 存在负环
                        f = 1;
                }
            }
        }
    }
    if(f) printf("-1\n");//存在负环
    else printf("%d\n",dis[n]);
}
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m) != EOF)
    {
        for(int i=1;i<=n;i++) first[i] = -1;
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d%d",&u[i],&v[i],&w[i]);
            next[i] = first[u[i]];
            first[u[i]] = i;
        }
        spfa(1,n);
    }
    return 0;
}