ZOJ 2966 Build The Electric System【最小生成树】

//2632030 	2011-08-18 16:57:56 	Accepted 	2966 	C++ 	0 	1652 	ylwh@Unknown
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
using namespace std;
#define N 501
struct edge
{
	int x, y, cost;
}e[N * N / 2];
int root[N];
int find_root(int x)
{
	int temp = x;
	while(temp != root[temp])
		temp = root[temp];
	root[x] = temp;
	return temp;
}
int cmp(struct edge a, struct edge b)
{
	return a.cost < b.cost;
}
int main()
{
	int t, n, E, i, j, a, b, x, y, cnt, ans;
	scanf("%d", &t);
	while(t--)
	{
		cnt = -1;
		ans = 0;
		scanf("%d%d", &n, &E);
		for(i=0; i<n; i++)
			root[i] = i;
		for(i=0; i<E; i++)
		{
			scanf("%d%d%d", &x, &y, &j);
			if(j)
			{
				e[++cnt].x = x;
				e[  cnt].y = y;
				e[  cnt].cost = j;
			}
			else
			{
				a = find_root(x);
				b = find_root(y);
				if(a > b)
					root[a] = b;
				else if(a < b)
					root[b] = a;
			}
		}
		sort(e, e + cnt + 1, cmp);
		for(i=0; i<=cnt; i++)
		{
			a = find_root(e[i].x);
			b = find_root(e[i].y);
			if(a != b)
			{
				ans += e[i].cost;
				if(a > b)
					root[a] = b;
				else
					root[b] = a;
			}
		}
		printf("%d\n", ans);
	}
    return 0;
}