hdu2818 Building Block

John are playing with blocks. There are N blocks (1 <= N <= 30000) numbered 1...N。Initially, there are N piles, and each pile contains one block. Then John do some operations P times (1 <= P <= 1000000). There are two kinds of operation:

M X Y : Put the whole pile containing block X up to the pile containing Y. If X and Y are in the same pile, just ignore this command. 
C X : Count the number of blocks under block X 

You are request to find out the output for each C operation.

The first line contains integer P. Then P lines follow, each of which contain an operation describe above.

Output the count for each C operations in one line.

6
M 1 6
C 1
M 2 4
M 2 6
C 3
C 4

1
0
2

这题也是带权并查集，设三个数组pre[i],num[i](代表i所在集合的数字总数),root[i]表示i下面的数字总数。每次移动时输入两个数a,b,因为移动过程中a所在的所有数都移动到b所在集合所有数的上面，所以令a的祖先t1的父亲为b的祖先t2，这样下面递归的时候，root[i]可以递归相加。
#include<iostream>
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<algorithm>
#include<map>
#include<string>
using namespace std;
char s[10];
int pre[30005],num[30005],root[30005];
int find(int x)
{
	int temp;
	if(pre[x]==x)return x;
	temp=pre[x];
	pre[x]=find(pre[x]);
	root[x]+=root[temp];
	return find(pre[x]);
}

int main()
{
	int p,i,m,j,a,b,t1,t2;
	while(scanf("%d",&p)!=EOF)
	{
		for(i=0;i<=30005;i++){
			pre[i]=i;num[i]=1;root[i]=0;
		}
		while(p--)
		{
			scanf("%s",s);
			if(s[0]=='M'){
				scanf("%d%d",&a,&b);
				t1=find(a);t2=find(b);
				if(t1==t2)continue;
				pre[t1]=t2;
				root[t1]+=num[t2];
				num[t2]+=num[t1];
			}
			else if(s[0]=='C'){
				scanf("%d",&a);
				t1=find(a);
				printf("%d\n",root[a]);
			}
		}
	}
	return 0;
}