[最近公共祖先] POJ 1330 Nearest Common Ancestors

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
int num,frist[20010],node[20010],deep[20010],ancestor[20010][17],n;
struct mp
  {
  	 int to,next;
  }map[20010];
void init()
  {
  	 num=0;
  	 memset(ancestor,0,sizeof(ancestor));
  	 memset(frist,0,sizeof(frist));
  	 memset(deep,0,sizeof(deep));
  	 memset(node,0,sizeof(node)); 
  	 memset(map,0,sizeof(map));
  }
void add(int x,int y)
  {
  	 ++num;
  	 map[num].to=y;
  	 map[num].next=frist[x];frist[x]=num;
  }
void build(int v)
  {
  	 int i;
  	 for(i=frist[v];i;i=map[i].next)
  	   {
  	   	  if(!deep[map[i].to])
  	   	    {
  	   	      ancestor[map[i].to][0]=v; 
  	   	      deep[map[i].to]=deep[v]+1;
  	   	      build(map[i].to);
  	   	    }
	   }
  }
void init_ancestor()
  {
  	 int i,j;
  	 for(j=1;j<17;++j)
  	   for(i=1;i<=n;++i)
  	     if(ancestor[i][j-1])
  	       ancestor[i][j]=ancestor[ancestor[i][j-1]][j-1];
  	 return;
  }
int lca(int a,int b) 
  {
  	int i,dep;
  	if(deep[a]<deep[b]) swap(a,b);
  	dep=deep[a]-deep[b];
  	for(i=0;i<17;++i) if((1<<i)&dep) a=ancestor[a][i];
  	if(a==b) return a;
  	for(i=16;i>=0;--i)
  	  {
  	  	 if(ancestor[a][i]!=ancestor[b][i])
  	  	   {
  	  	   	  a=ancestor[a][i];
  	  	   	  b=ancestor[b][i];
		   }
	  }
	return ancestor[a][0];
  }
int main()
  {
  	 int T,i,v,w,roof,qv,qw;
  	 scanf("%d",&T);
  	 while(T--)
  	   {
  	   	  init();
  	   	  scanf("%d",&n);
  	   	  for(i=0;i<n-1;++i) 
  	   	    {
  	   	      scanf("%d%d",&v,&w);
  	   	      add(v,w);add(w,v);
  	   	      ancestor[w][0]=v;
  	   	      if(!ancestor[v][0]) roof=v;//找根，根不同答案是不同的。
			}
		  deep[roof]=1;
		  build(roof);
		  init_ancestor();
		  scanf("%d%d",&qv,&qw);
		  printf("%d\n",lca(qv,qw));
	   }
	 return 0;
  }