UVa 10608 Friends (求并查集中最大的集合的基数)

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=1549

思路：

先合并，再遍历每个元素，对其父亲元素计数+1

for (i = 1; i <= n; ++i)
	maxcnt = max(maxcnt, ++cnt[find(i)]);

完整代码：

/*0.049s*/

#include<bits/stdc++.h>
using namespace std;
const int mx = 30005;

int fa[mx], rk[mx], cnt[mx];

int find(int x) {return fa[x] == x ? x : fa[x] = find(fa[x]);}

void merge(int x, int y)
{
	x = find(x), y = find(y);
	if (x == y) return; ///已合并
	if (rk[x] < rk[y])
		fa[x] = y;
	else
	{
		fa[y] = x;
		if (rk[x] == rk[y]) ++rk[x];
	}
}

int main()
{
	int t, n, m, a, b, i, maxcnt;
	scanf("%d", &t);
	while (t--)
	{
		scanf("%d%d", &n, &m);
		fill(rk, rk + n, 1);
		for (int i = 1; i <= n; ++i) fa[i] = i;
		while (m--)
		{
			scanf("%d%d", &a, &b);
			merge(a, b);
		}
		maxcnt = 1;
		memset(cnt, 0, sizeof(cnt));
		for (i = 1; i <= n; ++i)
			maxcnt = max(maxcnt, ++cnt[find(i)]);
		printf("%d\n", maxcnt);
	}
	return 0;
}