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Discussion of Problem 1416. Confidential

Why this code gives WA#10?
Posted by Aram Shatakhtsyan 24 Apr 2007 22:34
Please help. It gives Wrong Answer on test 10.
Where is mistake? Maybe some tricky cases?

#include <stdio.h>
int m[505][505],n;
int Prim();
int main()
{
    int k,i,j,a,b,s,temp,x;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=n;j++)
        {
            m[i][j]=-1;
        }
    }
    for(i=0;i<k;i++)
    {
        scanf("%d%d%d",&a,&b,&s);
        m[a][b]=m[b][a]=s;
    }
    printf("Cost: ");
    x=Prim();
    if(x==1000000000) printf("-1\n");
    else printf("%d\n",x);
    s=1000000000;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<i;j++)
        {
            if(m[i][j]!=-1)
            {
                temp=m[i][j];
                m[i][j]=m[j][i]=-1;
                x=Prim();
                if(x<s) s=x;
                m[i][j]=m[j][i]=temp;
            }
        }
    }
    printf("Cost: ");
    if(s==1000000000) printf("-1\n");
    else printf("%d\n",s);
    return 0;
}
int Prim()
{
    int dist[505],i,parent[505],s=0,j,nom,d;
    dist[1]=0;
    for(i=2;i<=n;i++)
    {
        parent[i]=-1;
        if(m[i][1]!=-1) { parent[i]=1; dist[i]=m[i][1]; }
    }
    bool vis[505]={0};
    vis[1]=1;
    for(i=1;i<n;i++)
    {
        nom=-1;
        for(j=1;j<=n;j++)
        {
            if(!vis[j] && parent[j]!=-1 && (nom==-1 || dist[j]<d)) { nom=j; d=dist[j]; }
        }
        if(nom==-1) break;
        s+=d;
        vis[nom]=1;
        for(j=1;j<=n;j++)
        {
            if(!vis[j] && m[j][nom]!=-1 && (parent[j]==-1 || m[j][nom]<dist[j]))
            {
                dist[j]=m[j][nom];
                parent[j]=nom;
            }
        }
    }
    for(i=1;i<=n;i++)
    {
        if(!vis[i]) return 1000000000;
    }
    return s;
}