http://poj.org/problem?id=1287

#include<iostream>
#include<math.h>
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<algorithm>
#define maxn 106
#define INF 1000000
using namespace std;
int n,m;
int graph[maxn][maxn];
int lowcost[maxn];
int visited[maxn];
void createGraph()
{
    memset(graph,INF,sizeof(graph));
    memset(lowcost, 0, sizeof(lowcost));
    memset(visited, 0, sizeof(visited));
    int u,v,w;
    for(int i=1;i<=m;i++){
        cin>>u>>v>>w;
        if(graph[u][v]>w)
        {
            graph[u][v]=graph[v][u]=w;
        }//Prim 演算法需要進行判斷最小重邊
    }
}
void prim()
{
    int sum=0,cnt=0;
    visited[1]=1;
    for(int i=1;i<=n;i++){
        lowcost[i]=graph[1][i];
    }
    while(true)
    {
        int minn=lowcost[1];
        int index=1;
        for(int j=2;j<=n;j++){
            if(!visited[j]&&lowcost[j]<minn){
                minn=lowcost[j];
                index=j;
            }
        }
        if(index==1)break;
        sum+=minn;
        cnt++;
        visited[index]=1;
        for(int j=1;j<=n;j++){
            if(!visited[j]&&lowcost[j]>graph[index][j])
            {
                lowcost[j]=graph[index][j];
            }
        }
    }
    if(cnt==n-1)cout<<sum<<endl;
    else cout<<"?"<<endl;
}
int main()
{
    while(cin>>n>>m&&n)
    {
        createGraph();
        prim();

    }
    return 0;
}