HOJ 1863 畅通工程

并查集、最小生成树用Prime算法，注意细节即可

#include
#include
#include
#pragma warning(disable: 4996)
using namespace std;
const int NN = 100, INF = 99999999;
int a[NN][NN], f[NN];

int find(int x)
{//寻找根节点，即x点所在集合的标记值
	if (x == f[x]) return x;
	f[x] = find(f[x]);
	return f[x];
}

int mer(int x, int y)
{
	x = find(x);
	y = find(y);
	if (x != y)
		f[x] = y;
	return 1;
}

int main()
{
	int n, m, x, y, z, sum;
	while (cin >> m >> n && m)
	{
		sum = 0;
		for (int i = 1; i <= n; i++)
			f[i] = i;
		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= i; j++)
				a[i][j] = INF;
		while (m--)
		{
			scanf("%d %d %d", &x, &y, &z);
			if (z == 0) continue;
			x >= y ? a[x][y] = z : a[y][x] = z;
		}
		while (1)
		{
			int min0 = INF, flag = 1;
			for(int i = 1; i <= n; i++)
				for(int j = 1; j <= i; j++)
					if (find(i) != find(j) && a[i][j] < min0)
					{
						min0 = a[i][j];
						x = i;
						y = j;
						flag = 0;
					}
			if (flag) break;
			mer(x, y);
			sum += a[x][y];
		}//while
		int p = 1;
		for(int i = 2; i <= n; i++)//判断是否所有的村庄都属于同一个集合，不是的话说明不满足全部连通的条件，输出？
			if (find(i - 1) != find(i))
			{
				p = 0;
				break;
			}
		if (p)
			cout << sum << endl;
		else
			cout << "?" << endl;
	}
	return 0;
}