PKU1330+LCA

简单的LCA。。。

dfs里fa的判断很重要呀。。。亲。。。

/*
LCA
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
#include<queue>
#include<map>
#include<math.h>
using namespace std;
typedef long long ll;
//typedef __int64 int64;
const int maxn = 10005;
const int inf = 0x7fffffff;
const double pi=acos(-1.0);
const double eps = 1e-8;
int deep[ maxn ],ace[ maxn ],fa[ maxn ];
//int dis[ maxn ];
struct node{
    int u,next;
}edge[ maxn<<4 ];
int cnt,head[ maxn ];
void init(){
    cnt = 0;
    memset( fa,0,sizeof( fa ) );
    memset( head,-1,sizeof( head ) );
}
void addedge( int a,int b){
    edge[ cnt ].u = b;
    edge[ cnt ].next = head[ a ];
    head[ a ] = cnt++;
}
void dfs( int now,int now_father,int now_ace,int now_deep/*,int now_dis*/ ){
    fa[ now ] = now_father;
    ace[ now ] = now_ace;
    deep[ now ] = now_deep;
    //dis[ now ] = now_dis;
    for( int i=head[ now ];i!=-1;i=edge[ i ].next ){
        int v = edge[ i ].u;
        //if( fa[v]==0 ){
            dfs( v,now,now_ace,now_deep+1/*,now_dis+edge[ i ].val*/ );
        //}
    }
}
int find( int x,int y ){
    if( x==y ) return x;
    if( deep[x]>deep[y] ) return find( fa[x],y );
    else return find( x,fa[y] );
}
int main(){
    int ca;
    scanf("%d",&ca);
    while( ca-- ){
        int n;
        scanf("%d",&n);
        int a,b;
        init();
        for( int i=0;i<n-1;i++ ){
            scanf("%d%d",&a,&b);
            addedge( a,b );
        }
        scanf("%d%d",&a,&b);
        for( int i=1;i<=n;i++ ){
            if( fa[i]==0 ){
                dfs( i,-1,i,0/*,0*/ );
            }
        }
        /*
        for( int i=1;i<=n;i++ ){
            printf("fa[%d]=%d\n",i,fa[i]);
        }
        */
        int father = find( a,b );
        printf("%d\n",father);
    }
    return 0;
}