hdu1232

hdu1232

畅通工程

0x00 Tags

并查集

0x01 题目简介

统计总的根节点个数ans，然后减1就是结果

0x02 代码

#include<bits/stdc++.h>

using namespace std;


const int maxn = 1010;

int root[maxn];


void Init()
{
	for (int i = 1; i < maxn; i++)
	{
		root[i] = i;
	}
}

/*

未优化的查找

int Find(int x)
{
	//return x == root[x] ? x : Find(root[x]);

	while (x != root[x])
	{
		x = root[x];
	}

	return x;
}

*/


int Find(int x)
{
	//return x == root[x] ? x : Find(root[x]);

	int r = x;

	while (r != root[r])
	{
		r = root[r];
	}

	int i = x, j;
	while (i != r)
	{
		j = root[i];
		root[i] = r;
		i = j;
	}

	return r;
}


void Union(int x, int y)
{
	x = Find(x);
	y = Find(y);

	if (x != y) root[x] = y;
}



int main()
{
	
	int n, m;
	while (scanf("%d", &n) != EOF)
	{
		if (n == 0) break;

		Init();

		int s, t;

		scanf("%d", &m);

		for (int i = 1; i <= m; i++)
		{
			scanf("%d%d", &s, &t);
			Union(s, t);
		}

		// 找出连通分量的个数
		int num = 0;

		for (int i = 1; i <= n; i++)
		{
			if (root[i] == i)
				num++;

		}

		printf("%d\n", num - 1);
	}

	return 0;
}