No.5 - POJ1861 克鲁斯卡尔 MST 边贪心 并查集

kruskal算法：

// ShellDawn
// POJ1861
// No.5

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define MM(x) memset(x,0,sizeof(x))
using namespace std;

#define maxn 1005
#define maxm 15005
int n,m;
struct Node{
    int a;
    int b;
    int v;
};
Node E[maxm];
int fa[maxn];
int ans[maxn][2];
int cnt = 0;

bool cmp(const Node& x,const Node& y){
    if(x.v < y.v) return true;
    return false;
}

int findfa(const int& x){
    int y = x;
    while(fa[y] != y) y = fa[y];
    int z = y;
    y = x;
    while(fa[y] != y){
        int t = fa[y];
        fa[y] = z;
        y = t;
    }
    return z;
}

bool join(const int& x,const int& y){
    int fx = findfa(x);
    int fy = findfa(y);
    if(fx == fy) return false;
    if(fx > fy) swap(fx,fy);
    fa[fy] = fx;
    return true;
}

void solve(){
    int num = n;
    for(int i=0;i<m;i++){
        if(join(E[i].a,E[i].b)){
            num --;
            ans[cnt][0] = E[i].a;
            ans[cnt][1] = E[i].b;
            cnt++;
        }
        if(num == 1){
            printf("%d\n%d\n",E[i].v,n-1);
            break;
        }
    }
    for(int i=0;i<cnt;i++){
        printf("%d %d\n",ans[i][0],ans[i][1]);
    }
}

int main(){
    while(~scanf("%d%d",&n,&m)){
        cnt = 0;
        for(int i=0;i<=n;i++) fa[i] = i;
        for(int i=0;i<m;i++){
            scanf("%d%d%d",&E[i].a,&E[i].b,&E[i].v);
        }
        sort(E,E+m,cmp);
        solve();
    }
    return 0;
}