HDU3367

题意为求一个最大森林，使这个森林里面至多有1个环

用类似Kruskal的用法求一颗最大生成树，用mark数组标记是否带环

#include <iostream>
#include<cstdio>
#include<cstring>
#include<cstring>
#include<algorithm>
#define N  100005
using namespace std;
int mark[N],vis[N],fa[N],ans,rank[N];
int m,n;
struct Edge{
    int u,v;
    int w;
}edge[N];
bool cmp(Edge a,Edge b){
    return a.w>b.w;
}
void init(){
    for(int i=0;i<n;i++){
    fa[i]=i;
    rank[i]=1;
    mark[i]=0;
    }
}
int find(int x){
    if(fa[x]==x)
    return x;
    return find(fa[x]);
}
void merge(int u,int v,int w){
    int fx,fy;
    fx=find(u);
    fy=find(v);
    if(fx==fy){
        if(!mark[fx]){
         mark[fx]=1;
         ans+=w;
        }
    }
    else {
        if(!mark[fx]||!mark[fy]){
            if(rank[fx]>rank[fy]){
                fa[fy]=fx;
                mark[fx]=(mark[fx]||mark[fy]);
                rank[fx]+=rank[fy];
            }
            else{
                fa[fx]=fy;
                rank[fy]+=rank[fx];
                mark[fy]=(mark[fx]||mark[fy]);
            }
            ans+=w;
        }
    }
}
int main()
{
    int i,cnt;
    while(scanf("%d%d",&n,&m)!=EOF,n){
        ans=0;
        for(i=0;i<m;i++){
            scanf("%d%d%d",&edge[i].u,&edge[i].v,&edge[i].w);
        }
        sort(edge,edge+m,cmp);
        init();
        for(i=0;i<m;i++){
            merge(edge[i].u,edge[i].v,edge[i].w);
        }
        printf("%d\n",ans);
    }
    return 0;
}