1115. Counting Nodes in a BST (30)

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本文提供了一种高效的方法来计算二叉搜索树(BST)中特定层级的节点数量。通过使用递归和层序遍历技术，该算法可以快速确定BST中最底层及其上一层的节点数目。

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1115. Counting Nodes in a BST (30)
2017.9.6更新
看了一下以前做的，做复杂了orz，下面为新更新AC代码

#include <iostream>
#include <cstdio>
#include <functional>
using namespace std;
struct TreeNode
{
    int val;
    TreeNode *left,*right;
    TreeNode(int x):val(x),left(NULL),right(NULL){}
};
void insert(int val,TreeNode *&r)
{
    if(r==NULL)
    {
        TreeNode *p=new TreeNode(val);
        r=p;
        return;
    }
    else if(r->val<val)
        insert(val,r->right);
    else
        insert(val,r->left);
}
void solve(TreeNode *r,int lev,const int lowest,int &n1,int &n2)
{
    if(r==NULL) return;
    if(lev==lowest) n1++;
    if(lev==lowest-1) n2++;
    solve(r->left,lev+1,lowest,n1,n2);
    solve(r->right,lev+1,lowest,n1,n2);
}
int main(int argc, char const *argv[])
{
    int n,val;
    TreeNode *r=NULL;
    cin>>n;
    while(n--)
    {
        cin>>val;
        insert(val,r);
    }
    function<int(TreeNode*)> h=[&h](TreeNode *r){return r==NULL?0:max(h(r->left),h(r->right))+1;};
    int lowest=h(r);
    int n1=0,n2=0;
    solve(r,1,lowest,n1,n2);
    printf("%d + %d = %d",n1,n2,n1+n2);
    return 0;
}

（以前AC代码）
考察层序遍历

#include <stdio.h>
#include <malloc.h>
int n1,n2;
struct Node
{
    struct Node *left,*right;
    int data;
}*T=NULL;
void CreatBST(struct Node **T,int v)
{
    if(*T)
    {
        if(v>(*T)->data)CreatBST(&(*T)->right,v);
        else CreatBST(&(*T)->left,v);
    }
    else
    {
        (*T)=(struct Node*)malloc(sizeof(struct Node));
        (*T)->left=(*T)->right=NULL;
        (*T)->data=v;
    }
}
void GetHeight(struct Node *T,int level,int *height)
{
    if(T)
    {
        *height=(level>*height)?level:*height;
        GetHeight(T->left,level+1,height);
        GetHeight(T->right,level+1,height);
    }
}
void GetN1AndN2(struct Node *T,int height)
{
    struct Node *queue[10000],*s;
    int front=0,rear=0,first=0,last=1,h=0,cnt=1;
    queue[rear++]=T;
    while(front!=rear)
    {
        s=queue[front++];
        ++first;
        if(s->left){queue[rear++]=s->left;++cnt;}
        if(s->right){queue[rear++]=s->right;++cnt;}
        if(first==last)
        {
            ++h;last=cnt;
            if(h==height-2)n2=cnt-first;
            if(h==height-1)n1=cnt-first;
        }
    }
}
int main()
{
    int n,height=0;
    scanf("%d",&n);
    for(int i=0;i<n;++i)
    {
        int v;
        scanf("%d",&v);
        CreatBST(&T,v);
    }
    GetHeight(T,1,&height);
    if(height==1)printf("1 + 0 = 1");
    else if(height==2)printf("%d + 1 = %d",n-1,n);
    else
    {
        GetN1AndN2(T,height);
        printf("%d + %d = %d\n",n1,n2,n1+n2);
    }
    return 0;
}