hdoj1863

Problem : 1863 ( 畅通工程 )     Judge Status : Accepted
RunId : 2690792    Language : G++    Author : huwenbiao
Code Render Status : Rendered By HDOJ G++ Code Render Version 0.01 Beta

/***************************************************************\
 *Author:Hu Wenbiao
 *Created Time: Mon 26 Jul 2010 08:09:32 PM CST
 *File Name: main.cpp
 *Description:最小生成树。Kruscal算法
\***************************************************************/
//*========================*Head File*========================*\\

#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<algorithm>
#include<string.h>
/*----------------------*Global Variable*----------------------*/
int parent[110],N,M,sum;
struct Edge{
    int from,to,dis;
}edge[110];
//*=======================*Main Program*=======================*//
using namespace std;
bool cmp(Edge a,Edge b){
    return a.dis<b.dis;
}
int find(int x){
if(parent[x]>0)
      parent[x]=find(parent[x]);
    return parent[x]>0?parent[x]:x;
}
void union_set(int x,int y){
    x=find(x),y=find(y);
    if(parent[x]<parent[y]){
        parent[x]+=parent[y];
        parent[y]=x;
    }
    else{
        parent[y]+=parent[x];
        parent[x]=y;
    }
}
int main(){
    //freopen("input","r",stdin);
    while(scanf("%d%d",&N,&M)!=EOF&&N){
        for(int i=0;i<N;i++){
            scanf("%d%d%d",&edge[i].from,&edge[i].to,&edge[i].dis);
        }
        if(M>N+1){//剪枝
            printf("?\n");
            continue;
        }
        sum=0;
        memset(parent,-1,sizeof(parent));
        sort(edge,edge+N,cmp);
        for(int i=0;i<N;i++){
            int x=find(edge[i].from),y=find(edge[i].to);
            if(x!=y){
                union_set(x,y);
                sum+=edge[i].dis;
                M--;
            }
        }
        if(M==1)
          printf("%d\n",sum);
        else
          printf("?\n");
    }
}