並查集【模版】（洛谷P3367）

初始化

int clear()
{
	for(int i = 1;i <= n;i ++)
		fa[i] = i;
	return 0;
}

尋找祖先

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

優化 ——路徑壓縮

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

合併兩個元素

int merge(int x,int y)
 

{
	int xx = find(x);
	int yy = find(y);
	if(xx == yy)return 0;
	fa[xx] = yy;
	return 1;
}

優化——按秩合併

int merge(int x,int y)
{
	int xx = fin(x);
	int yy = find(y);
	if(xx == yy)return 0;
	if(h[xx] < h[yy])
	{
		fa[xx] = yy;
		h[yy] = h[xx] + 1;
	}
	else
	{
		fa[yy] = xx;
		h[xx] = h[yy] + 1;
	}
	return
 
 1;
}

最後綜合一下

#include <iostream>
#include <cstdio>

using namespace std;

int fa[2357],n,m,k,x,y,h[2357];

int clear()
{
	for(int i =1; i <= n; i ++)
		fa[i] = i;
}

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

int merge(int x,int y)
{
	int xx = find
 
(x);
	int yy = find(y);
	if(xx == yy)return 0;
	if(h[xx] <= h[yy])
	{
		fa[xx] = yy;
		h[yy] = h[xx] + 1;
	}
	else
	{
		fa[yy] = xx;
		h[xx] = h[yy] + 1;
	}
	return 1;
}

int main()
{
	scanf("%d%d",&n,&m);
	clear();
	while(m --)
	{
		scanf("%d%d%d",&k,&x,&y);
		if(k == 1)
		{
			merge(x,y);
		}
		if(k == 2)
		{
			if(find(x) == find(y))printf("Y\n");
				else printf("N\n");
		}
	}
	return 0;
}

P.S. 這裡沒有采用按秩合併是因為該優化有一定的侷限性，像“銀河英雄傳說”就不能按秩合併。