Kruscal算法1.4

http://poj.org/problem?id=1251

给定一个图中的节点,节点用字母表示,求最小生成树

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#define maxn 102
#define INF 1000000
using namespace std;
struct node
{
    int u;
    int v;
    int w;
    node()
    {
        w=1000000;
    }
}edge[500000];
int pre[10000];
int n,m;
bool cmp(const node&a,const node&b )
{
    return a.w<b.w;
}
int find(int x)
{
    return x==pre[x]?x:pre[x]=find(pre[x]);
}
void unions(int x,int y)
{
    int fx=find(x);
    int fy=find(y);
    if(fx!=fy)
    {
        pre[fx]=fy;
    }
}
void createGraph()
{
    memset(pre,0,sizeof(pre));
    char a,b,c;
    for(int i=1; i<=n; i++)
    {
        int k;
        cin>>a;
        cin>>k;
        for(int j=1; j<=k; j++)
        {
            cin>>b;
            int w;
            cin>>w;
            edge[++m].u=a-'A'+1;
            edge[m].v=b-'A'+1;;
            edge[m].w=w;
        }
    }
    for(int i=1; i<=n; i++)pre[i]=i;
}
int kruscal()
{

    int ans=0,ans1=0;
    sort(edge+1,edge+m+1,cmp);
    for(int i=1; i<=m; i++)
    {
        if(find(edge[i].u)!=find(edge[i].v))
        {
            unions(edge[i].u,edge[i].v);
            ans1++;
            ans+=edge[i].w;
        }
    }
    if(ans>=n-1)return ans;
    return -1;
}
int main()
{
    while(cin>>n&&n!=0)
    {
        n--;
        m=0;
        createGraph();
        cout<<kruscal()<<endl;

    }
}