POJ1287

这道题顶点少，边多，属于稠密图，适合使用prime算法求解最小生成树 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=55;
const int inf=0x3f3f3f;
int mapp[maxn][maxn];
int vis[maxn];
int dis[maxn];
int n,m,from,to,weight,ans;
void init()
{
    ans=0;
    memset(vis,0,sizeof(vis));
    memset(mapp,inf,sizeof(mapp));
}
void prime()
{
    for(int i=1; i<=n; i++)
        dis[i]=min(mapp[1][i],mapp[i][1]);
    dis[1]=0;
    vis[1]=1;
    for(int v=0; v<n-1; v++)
    {
        int minx=inf;
        int p=-1;
        for(int i=1; i<=n; i++)
            if(!vis[i]&&dis[i]<minx)
            {
                p=i;
                minx=dis[i];
            }
        ans+=dis[p];
        vis[p]=1;
        for(int i=1; i<=n; i++)
            if(!vis[i]&&dis[i]>min(mapp[p][i],mapp[i][p]))
                dis[i]=min(mapp[p][i],mapp[i][p]);
    }
}
int main()
{
    while(scanf("%d",&n)&&n)
    {
        scanf("%d",&m);
        init();
        for(int i=0; i<m; i++)
        {
            scanf("%d%d%d",&from,&to,&weight);
            mapp[from][to]=min(weight,mapp[from][to]);
        }
        prime();
        printf("%d\n",ans);
    }
    return 0;
}