POJ1988 并查集(3)

1 题意

2 分析

在Find()函数中，如果利用递归来更新相关信息，那么一定要注意递归基的使用，如本题更新node[x].under_number 总是利用 node[old].under_number，而node[old].under_number在上一层递归里会被更新，注意当old==root时的情况。

3

#include <iostream>
#include <stdio.h>
#include <string.h>

using namespace std;

const int maxn=3e4+10;
struct Node{
int all_number;
int under_number;
int parent;//s.t.   bottom
}node[maxn];
void Ini(){
for(int i=1;i<maxn;i++){
node[i].parent=i;
node[i].all_number=1;
node[i].under_number=0;
}
}
int Find(int x){
if(node[x].parent==x)   return x;
else{
int old=node[x].parent;
node[x].parent=Find(old);
node[x].under_number+=node[old].under_number;
return node[x].parent;
}
}
void Join(int p1,int p2){
node[p1].parent=p2;
node[p1].under_number=node[p2].all_number;
node[p2].all_number+=node[p1].all_number;
}
int main(){
int p,n1,n2,p1,p2;
char com[2];
while(~scanf("%d",&p)){
Ini();
for(int i=1;i<=p;i++){
scanf("%s",com);
if(com[0]=='M'){
scanf("%d%d",&n1,&n2);
p1=Find(n1);
p2=Find(n2);
if(p1!=p2)
Join(p1,p2);
}
else if(com[0]=='C'){
scanf("%d",&n1);
n2=Find(n1);
cout<<node[n1].under_number<<endl;
}
}
}
}