POJ1330 Nearest Common Ancestors

最新推荐文章于 2020-11-23 16:04:39 发布

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POJ1330

筱柒Littleseven
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题目链接

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>

using namespace std;

const int MAXN = 10010;

int tot,to[MAXN],nex[MAXN],head[MAXN];
int deep[MAXN],step,fa[MAXN],t,n,root;

void add(int x,int y){ to[++tot]=y; nex[tot]=head[x]; head[x]=tot; }
void dfs(int x,int step)
{
  deep[x]=step;
  for(int i=head[x]; i; i=nex[i]) dfs(to[i],step+1);
}
void setup()
{
  memset(head,0,sizeof head); 
  memset(to,0,sizeof to);
  memset(nex,0,sizeof nex);
  memset(deep,0,sizeof deep);
  memset(fa,0,sizeof fa);
}
int lca(int x,int y)
{
  if(deep[x]<deep[y]) swap(x,y);
  while(deep[x]>deep[y]) x=fa[x];
  while(x!=y) x=fa[x],y=fa[y];
  return x;
}
int main()
{
  cin>>t;
  for(int i=1; i<=t; i++)
  {
      int root; setup();
      tot=0;
      cin>>n;
      for(int j=1; j<n; j++)
      {
          int a,b; cin>>a>>b;
          add(a,b); fa[b]=a;
      }
      for(int k=1; k<=n; k++){ if(!fa[k]) root=k; }
      int qa,qb; cin>>qa>>qb; dfs(root,1);
      cout<<lca(qa,qb)<<endl;
  }
  return 0;
}