UVA 558 Wormholes

利用SPFA判负环。如果一个节点出队N次有负环这里记录一下

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
int cnt[1010];
bool inq[1010];
int d[1010];
int w[1010][1010],N,M;
vector<int>G[1010];
queue<int>q;
bool SPFA()
{
    memset(cnt,0,sizeof(cnt));
    memset(inq,false,sizeof(inq));
    memset(d,0x3f,sizeof(d));
    while (!q.empty()) q.pop();
    q.push(0); cnt[0]++;
    inq[0] = true; d[0] = 0;
    while (!q.empty())
    {
        int u = q.front(); q.pop();
        inq[u] = false;
        for (int i = 0; i < (int)G[u].size(); i++)
        {
            int v = G[u][i];
            if (d[v] > d[u] + w[u][v])
            {
                d[v] = d[u] + w[u][v];
                if (!inq[v])
                {
                    inq[v] = true;
                    cnt[v]++;
                    if (cnt[v] >= N) return true;
                    q.push(v);
                }
            }
        }
    }
    return false;
}
int main()
{
    //freopen("sample.txt","r",stdin);
    int T;
    scanf("%d",&T);
    while (T--)
    {
        scanf("%d%d",&N,&M);
        for (int i = 0; i < 1010; i++) G[i].clear();
        while (M--)
        {
            int u,v,we;
            scanf("%d%d%d",&u,&v,&we);
            G[u].push_back(v);
            w[u][v] =  we;
        }
        if (SPFA()) puts("possible");
        else puts("not possible");
    }
    return 0;
}