hdu1863 畅通工程

链接：http://acm.hdu.edu.cn/showproblem.php?pid=1863
分析：裸的kruskal

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<vector>
#include<bitset>

using namespace std;
struct Edge
{
    int start,end,length;
    bool visit;
}edge[110000];
int cmp(Edge a,Edge b)
{
    return a.length<b.length;
}
int father[1100];
int n,m;
int num;
int find(int x)
{
    if (father[x]==x) return x;
    father[x]=find(father[x]);
    return father[x];
}
bool Union(int x,int y)
{
    int f1=find(x);
    int f2=find(y);
    if (f1==f2) return false;
    num++;
    if (f1<f2) father[f1]=f2;
        else   father[f2]=f1;
    return true;
}
int kruskal(int n,int m)
{
    int i,j=0;
    int sum=0;
    for (i=0;i<n;i++) father[i]=i;
    sort(edge,edge+m,cmp);
    for (i=0;i<m&&j<n;i++)
    {
        if (Union(edge[i].start,edge[i].end))
        {
            sum+=edge[i].length;
            edge[i].visit=1;
            j++;
        }
    }
    return sum;
}
int main()
{
    while (scanf("%d %d",&m,&n)==2&&m)
    {
        num=0;
        for (int i=0;i<m;i++)
        {
            scanf("%d %d %d",&edge[i].start,&edge[i].end,&edge[i].length);
            edge[i].visit=false;
        }
        int ans=kruskal(n,m);
        if (num!=n-1) printf("?\n");
        else printf("%d\n",ans);
    }
    return 0;
}