PAT A 1115. Counting Nodes in a BST (30)【二叉排序树】

#include<cstdio>  
#include<iostream>  
#include<cstring>  
#include<algorithm>  
using namespace std;  
typedef long long LL;  
const int INF = 0x7FFFFFFF;  
const int maxn = 1e5 + 10;  
int n, cnt[maxn], a[maxn];  
int ch[maxn][2], root;  

void insert(int &x,int y)
{
    if(!x){x=y;return;}
    if(a[y]<=a[x])insert(ch[x][0],y);
    else insert(ch[x][1],y);
}

void dfs(int x,int dep)
{
    if(!x)return;
    cnt[dep]++;
    dfs(ch[x][0],dep+1);
    dfs(ch[x][1],dep+1);
}
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
        insert(root,i);
    }
    dfs(root,1);
    for(int i=n;i;i--)
    {
        if(cnt[i])
        {
            printf("%d + %d = %d\n",cnt[i],cnt[i-1],cnt[i]+cnt[i-1]);
            break;
        }
    }
    return 0;
}