POJ 水题 1330 LCA

#include<iostream>
using namespace std;

const int maxn=10001;
int pre[maxn];

int main()
{
freopen("in.txt","r",stdin);
int t,n,a,b;
scanf("%d",&t);
while(t--){
scanf("%d",&n);
memset(pre,0,sizeof(pre));
for(int i=0;i<n-1;i++){
int a,b;
scanf("%d%d",&a,&b);
pre[b]=a;
}
scanf("%d%d",&a,&b);
int la=0,lb=0;
int p1=a,p2=b;
while(pre[p1]){p1=pre[p1];la++;}
while(pre[p2]){p2=pre[p2];lb++;}
p1=a,p2=b;
if(la>lb){
while(la>lb){la--;a=pre[a];}
}else{
while(lb>la){lb--;b=pre[b];}
}
while(la--){
if(a==b)break;
a=pre[a];
b=pre[b];
}
printf("%d\n",a);
}
}