1251 最小生成树模板题（prim）

注意初始化的cost矩阵，cost[i][i]=0,相互的那个也要初始化

/* ***********************************************
Author        :PeterBishop
Created Time  :Tue 19 Feb 2019 22:52:00 CST
File Name     :t.cpp
Origin        :P O J  1251
************************************************ */

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <queue>
#include <set>
#include <map>
int N;
using namespace std;
const int MAXN=30;
const int INF=0x3f3f3f3f;
bool vis[MAXN];
int lowc[MAXN];
int prim(int cost[][MAXN],int n){
    int ans=0;
    memset(vis,false,sizeof(vis));
    vis[0]=true;
    for(int i=1;i<n;i++)
        lowc[i]=cost[0][i];
    for(int i=1;i<n;i++){
        int minc=INF;
        int p=-1;
        for(int j=0;j<n;j++)
            if(!vis[j]&&minc>lowc[j]){
                minc=lowc[j];
                p=j;
            }
            if(minc==INF)
                return -1;
            ans+=minc;
            vis[p]=true;
            for(int j=0;j<n;j++)
                if(!vis[j]&&lowc[j]>cost[p][j])
                    lowc[j]=cost[p][j];
        }
        return ans;
    }
int main()
{
    //freopen("out.txt","w",stdout);
    freopen("in.txt","r",stdin);
    while(cin>>N){
        if(N==0)
            break;
        int cost[MAXN][MAXN];
        for(int i=0;i<MAXN;i++)
            for(int j=0;j<MAXN;j++)
                cost[i][j]=i==j?0:INF;
        for(int i=0;i<N-1;i++){
            char a;
            int k;
            cin>>a>>k;
            for(int j=0;j<k;j++){
                char x;
                int m;
                cin>>x>>m;
                cost[a-'A'][x-'A']=cost[x-'A'][a-'A']=m;
            }
        }
        cout<<prim(cost,N)<<endl;



    }



    return 0;
}