hdoj1879 继续畅通工程

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1879

最小生成树，只要注意先把已经修好的路先合并了

//prim算法模版 只要改变一点点就可以了
//开始使用cin输入，结果TLE了
#include <iostream>
#include <algorithm>
using namespace std;
struct Road {
	int c1, c2, cost, isbuilt;
};
Road road[5051];
int city[101];
int cmp (const Road a, const Road b)
{
	return a.cost < b.cost;
}
int Find(const int n)
{
	if (city[n] == -1)
		return n;
	return city[n] = Find(city[n]);
}
int Merge(const int a, const int b)
{
	int x = Find(a);
	int y = Find(b);
	if (x == y) return 0;
	if (x < y) city[y] = x;
	else city[x] = y;
	return 1;
}
int main()
{
	int n, m;
	int sum, count, i;
	while (scanf("%d", &n) && n) {
		m = n*(n-1)/2;
		memset(city, -1, sizeof(city));
		sum = count = 0;
		for (i = 0; i < m; i++) {
			scanf("%d%d%d%d", &road[i].c1, &road[i].c2, &road[i].cost, &road[i].isbuilt);
			if (road[i].isbuilt) {
				if(Merge(road[i].c1, road[i].c2))
					count ++;
			}
		}
		sort(road, road+m, cmp);
		for (i = 0; i < m; i++) {
			if (count == n-1) break;
			if (!road[i].isbuilt && Merge(road[i].c1, road[i].c2)) {
				sum += road[i].cost;
				count ++;
			}
		}
		cout << sum << endl;
	}
	return 0;
}