第一个居然是spfa 0.072

第二个才是bellman-ford 0.046

/**
*   又是大水。。再来测试测试bellman-ford和spfa的效率。。
*   居然。。。bellman-ford比spfa要快好多。。。 求解释？
*   附加floyd判负权环。其实原来和bellman一样。
*/

#include <cstdio>
#include <iostream>
#include <cstring>
#include <cmath>
#include <string>
#include <queue>
#include <map>
#include <vector>
#include <algorithm>
#define DEBUG 0
#define INF 0x1fffffff
#define MAXS 2005

typedef long long LL;
using namespace std;

int u[MAXS], v[MAXS], t[MAXS];
int dis[MAXS], inq[MAXS], times[MAXS];
int n, m;
struct Edge
{
    int v, t;
    Edge() {}
    Edge(int vv, int tt) {v = vv; t = tt;}
};
vector<Edge> ver[MAXS];

int cnt = 0;
bool bellman()
{
    for(int i = 0; i < n; i ++) {
        dis[i] = INF;
    }
    dis[0] = 0;
    for(int k = 0; k < n - 1; k ++)
    for(int i = 0; i < m; i ++)
    {
        if(dis[u[i]] != INF && dis[v[i]] > dis[u[i]] + t[i])
            dis[v[i]] = dis[u[i]] + t[i];
    }

    for(int i = 0; i < m; i ++)
    {
        if(dis[u[i]] != INF && dis[v[i]] > dis[u[i]] + t[i])
            return true;
    }

    return false;
}

bool spfa()
{
    queue<int> q;
    for(int i = 0; i < n; i ++) {
        inq[i] = 0;
        times[i] = 0;
        dis[i] = INF;
    }
    inq[0] = 1;
    dis[0] = 0;
    q.push(0);
    while(!q.empty())
    {
        int cur = q.front(); q.pop();
        times[cur] ++;
        inq[cur] = 0;
        if(times[cur] > n) return true;
        for(int i = 0; i < ver[cur].size(); i ++)
        {
            int vv = ver[cur][i].v, tt = ver[cur][i].t;
            if(dis[cur] != INF && dis[vv] > dis[cur] + tt)
            {
                dis[vv] = dis[cur] + tt;
                if(!inq[vv]) {
                    inq[vv] = 1;
                    q.push(vv);
                }
            }
        }
    }
    return false;
}

int main()
{
    int cases;  scanf("%d", &cases);
    while(cases --)
    {
        scanf("%d%d", &n, &m);
        for(int i = 0; i < n; i ++)
            ver[i].clear();
        for(int i = 0; i < m; i ++) {
            int uu, vv, tt;
            scanf("%d%d%d", &uu, &vv, &tt);
            ver[uu].push_back(Edge(vv, tt));
        }
        if(spfa()) printf("possible\n");
        else printf("not possible\n");
    }
    return 0;
}

/**
bool floyd()
{
    for(int k = 0; k < n; k ++) {
        for(int i = 0; i < n; i ++)
        {
            for(int j = 0; j < n; j ++) {
                if(gra[i][j] > gra[i][k] + gra[k][j])
                    gra[i][j] = gra[i][k] + gra[k][j];
            }
        }
        for(int i = 0; i < n; i ++)
            for(int j = 0; j < n; j ++) {
                if(gra[i][j] > gra[i][k] + gra[k][j])
                    return true;
            }
    }
    return false;
}
*/