POJ 3259 Wormholes（负权环路）

#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#define rep(i,a,b) for(int i = a; i < b; i++)
#define _rep(i,a,b) for(int i = a; i <= b; i++)
using namespace std;
#define inf 0x3f3f3f3f
const int maxn = 1000, maxm = 10000;
int N,M,W;
struct E
{
    int v, time, nxt;
}Edge[maxm];

int cnt = 0;
int head[maxn], enter_cnt[maxn];
int dis[maxn], vis[maxn];
void add_edge(int u , int v, int d){
    Edge[cnt].v = v;
    Edge[cnt].time = d;
    Edge[cnt].nxt = head[u];
    head[u] = cnt++;
}
bool spfa(){
    fill(dis, dis+maxn, inf);
    memset(vis, 0, sizeof(vis));
    memset(enter_cnt, 0, sizeof(enter_cnt));
    queue<int> q;
    q.push(1);
    dis[1] = 0;
    vis[1] = 1;
    enter_cnt[1]++;
    while(!q.empty()){
        int u = q.front();
        for(int i = head[u]; i != -1; i = Edge[i].nxt){
            int v = Edge[i].v, d = Edge[i].time;
            if(dis[v] > dis[u] + d){
                if(++enter_cnt[v] >= N) return false; //如果入队次数 >= N， 那么一定有负权环路 
                dis[v] = dis[u] + d;
                if(!vis[v]){
                    vis[v] = 1;
                    q.push(v);
                }
            }
        }
        vis[u] = 0;
        q.pop();
    }
    return true;
}
int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        memset(head, -1, sizeof(head));
        cnt = 0;

        scanf("%d %d %d", &N, &M, &W);
        for(int i = 0; i < M; i++)
        {
            int tu,tv,tt;
            scanf("%d %d %d", &tu, &tv, &tt);
            add_edge(tu,tv,tt);
            add_edge(tv,tu,tt);
        }
        for(int i = 0; i < W; i++)
        {
            int tu,tv,tt;
            scanf("%d %d %d", &tu, &tv, &tt);
            add_edge(tu,tv,-tt);
        }

        if(!spfa()) printf("YES\n");
        else printf("NO\n");
    }
}