求助

#include<iostream>//P2009
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<queue>
using namespace std;
const int INF=123456789;
int f[50][50];
bool vis[50];
int dis[50];
int main()
{
    int n,m,i,j,k,minn=INF;
    char st,ed;
    cin>>n>>m;
    memset(f,INF,sizeof(f));
    memset(vis,false,sizeof(vis));
    for(i=1;i<n;i++)
    {cin>>j;f[i][i+1]=f[i+1][i]=j;}
    cin>>j;
    f[n][1]=f[1][n]=j;
    for(i=1;i<=m;i++)
    {
	 cin>>st>>ed>>j;
     if(f[st-'@'][ed-'@']==INF)
	  f[st-'@'][ed-'@']=f[ed-'@'][st-'@']=j;
	 if(j>f[st-'@'][ed-'@'])
	  f[st-'@'][ed-'@']=f[ed-'@'][st-'@']=j;
	}
    cin>>st>>ed;
	st-='@';ed-='@';
    for(i=1;i<=n;i++)dis[i]=f[st][i];
    dis[st]=INF;
    vis[st]=true;
    for(i=1;i<n;i++)
    {
        minn=INF;k=0;
        for(j=1;j<=n;j++)if(minn>dis[j]&&!vis[j]){minn=dis[j];k=j;}
        vis[k]=true;if(k==0)break;
        for(j=1;j<=n;j++)if(dis[k]+f[k][j]<dis[j])dis[j]=dis[k]+f[k][j];
    }
    cout<<dis[ed];
    return 0;
}