[] NOIP2018pj symmetrical binary tree

Face questions

https://www.luogu.org/problem/P5018

answer

#include<cstdio>
#include<iostream>
using namespace std;

struct node {
  int val,lson,rson;
} a[1050000];
int siz[1050000];
int n;

void dfs(int x){
  siz[x]=1;
  if (a[x].lson!=-1) dfs(a[x].lson),siz[x]+=siz[a[x].lson];
  if (a[x].rson!=-1) dfs(a[x].rson),siz[x]+=siz[a[x].rson];
}

bool can(int u,int v){
  if (u==-1 && v==-1) return true;
  if (u!=-1 && v!=-1) {
    if (a[u].val==a[v].val && can(a[u].lson,a[v].rson) && can(a[u].rson,a[v].lson))
      return true; else return false;
  }
  return false;
}

int main(){
  int i;
  scanf("%d",&n);
  for (i=1;i<=n;i++) scanf("%d",&a[i].val);
  for (i=1;i<=n;i++) scanf("%d %d",&a[i].lson,&a[i].rson);
  dfs(1);
  int ans=0;
  for (i=1;i<=n;i++) if (can(a[i].lson,a[i].rson)) ans=max(ans,siz[i]);
  printf("%d\n",ans);
}