poj 3259 Wormholes 负权边最短路

Problem:
判断是否存在负权环
Solution:
利用spfa算法

#include <iostream>#include<cstdio>#include <vector>#include <queue>#include <cstring>using namespace std;const int maxn = 510;const int INF = 0x3fffffff;struct Node{    int e, w;    Node(int ne, int nw) : e(ne),w(nw){}    Node(){}};vector<vector<Node> > G;int updateTimes[maxn];//判断是否有环int dist[maxn];bool spfa(int v, int n){//输入源点, 节点个数    for(int i = 1; i <= n; ++i)        dist[i] = INF;    dist[v] = 0;    queue<int> q;  q.push(v);    memset(updateTimes ,0,sizeof(updateTimes));    while(!q.empty()){        int s = q.front();  q.pop();        for(int i = 0; i < G[s].size(); ++i) {            int e = G[s][i].e;            if(dist[e] > dist[s] + G[s][i].w){                dist[e] = dist[s] + G[s][i].w;                q.push(e);                ++updateTimes[e];                if(updateTimes[e] >= n)                    return true;            }        }    }    return false;}int f,n,m,w;int main(){    scanf("%d",&f);    while(f--){        scanf("%d%d%d",&n,&m,&w);        G.clear();        G.resize(n+5);        int s,e,t;        for(int i = 0; i < m; ++ i) {            scanf("%d%d%d", &s, &e, &t);            G[s].push_back(Node(e,t));            G[e].push_back(Node(s,t));        }        for(int i = 0;i < w; ++i) {            scanf("%d%d%d", &s, &e, &t);            G[s].push_back(Node(e,-t));        }        if(spfa(1, n))            printf("YES\n");        else            printf("NO\n");    }    return 0;}