poj 2263 Heavy Cargo(floyd)

floyd
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<string>
#include<map>
#include<iostream>
using namespace std;
int n,m,edge[250][250],vis[250],dist[250];
map<string,int>a;

void floyd()
{
    int i,j,k,t;
    for(k=1; k<=n; k++)
        for(i=1; i<=n; i++)
            for(j=1; j<=n; j++)
            {
                if(edge[i][k]==-1||edge[k][j]==-1) continue;
                t=min(edge[i][k],edge[k][j]);
                if(edge[i][j]==-1) edge[i][j]=t;
                else if(edge[i][j]<t) edge[i][j]=t;
            }
}

int main()
{
    int i,j,tot,st,ed,cas=0,u,v,w;
    string s1,s2;
    while(~scanf("%d%d",&n,&m))
    {
        memset(edge,0,sizeof(edge));
        if(n==0&&m==0) break;
        a.clear();
        tot=1;
        for(i=0; i<m; i++)
        {
            cin>>s1>>s2>>w;
            if(a[s1]==0)
            {
                a[s1]=tot;
                tot++;
            }
            if(a[s2]==0)
            {
                a[s2]=tot;
                tot++;
            }
            u=a[s1];
            v=a[s2];
            edge[u][v]=w;
            edge[v][u]=w;
        }
        for(i=1; i<=n; i++)
            for(j=1; j<=n; j++)
            {
                if(edge[i][j]==0) edge[i][j]=-1;
            }
        cin>>s1>>s2;
        st=a[s1];
        ed=a[s2];
        floyd();
        printf("Scenario #%d
",++cas);
        printf("%d tons

",edge[st][ed]);
    }
    return 0;
}