uva 558

判断是否有负环。。。Bellman_ford

#include <algorithm>
#include <cstring>
#include <cstdio>
#define N 2200
#define INF 9999999

int v[N],w[N],u[N];
int d[N];
int n,m;
bool Bellman_ford()
{
    for(int i=0; i<n; ++i)
        d[i]=INF;
    d[0]=0;
    for(int k=0; k<n-1; ++k)
    {
        for(int i=0; i<m; ++i)
        {
            int x=u[i],y=v[i];
            if(d[x]<INF)
            {

                d[y]=d[y]<(d[x]+w[i])?d[y]:(d[x]+w[i]);printf("%d=%d,%d=%d\n",x,d[x],y,d[y]);
            }
        }
    }
    for(int i=0; i<m; ++i)
    {
        int x=u[i],y=v[i];
        if(d[y]>d[x]+w[i])
        {
            printf("%d %d %d %d %d %d\n",x,y,d[y],d[x]+w[i],d[x],w[i]);
            return true;
        }
    }
    return false;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d %d",&n,&m);
        for(int i=0; i<m; ++i)
        {
            scanf("%d %d %d",&u[i],&v[i],&w[i]);
        }
        if(Bellman_ford())
            puts("possible");
        else puts("not possible");
    }
    return 0;
}