POJ 2377 Bad Cowtractors

http://poj.org/problem?id=2377

裸求最大生成树

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <queue>
#include <algorithm>
#define READ() freopen("in.txt", "r", stdin);
#define MAXV 10007
#define MAXE 40007
#define INF 0x3f3f3f3f
using namespace std;

int N,M, num = 0;
struct Edge
{
    int from, to, cost;
    Edge () {}
    Edge (int from, int to, int cost) : from(from), to(to), cost(cost) {}
}edge[MAXE];

int par[MAXV];

int find(int x)
{
    if (par[x] == x) return x;
    else return par[x] = find(par[x]);
}

void unite(int x, int y)
{
    int px = find(x), py = find(y);
    if (px == py) return ;
    par[py] = px;
}

bool same(int x, int y)
{
    int px = find(x), py = find(y);
    return px == py;
}

bool cmp(Edge e1, Edge e2)
{
    return e1.cost > e2.cost;
}
int Kruskal()
{
    int res = 0;
    for (int i = 1; i <= N; i++) par[i] = i;
    sort(edge, edge+num, cmp);
    for (int i = 0; i < num; i++)
    {
        Edge e = edge[i];
        if (!same(e.from, e.to))
        {
            res += e.cost;
            unite(e.from, e.to);
        }
    }
    for (int i = 1; i <= N; i++)//判断一下是否都连通
    {
        for (int j = 1; j <= N; j++)
        {
            if (!same(i,j)) return -1;
        }
    }
    return res;
}


int main()
{
    READ()
    scanf("%d%d", &N, &M);
    for (int i = 0; i < M; i++)
    {
        int from, to, cost;
        scanf("%d%d%d", &from, &to, &cost);
        edge[num++] = Edge(from, to, cost);
        edge[num++] = Edge(to, from, cost);
    }
    int ans = Kruskal();
    cout << ans << endl;
}