1115 Counting Nodes in a BST

Posted 2021-10-05 CSU迦叶

我的DFS

void DFS(Node* root){
	if(root==NULL)return;
	
	if(root->lchild){
		root->lchild->layer = root->layer+1;
		cnt[root->lchild->layer] ++;
		maxLayer = max(maxLayer,root->lchild->layer);
		DFS(root->lchild);
	}
	if(root->rchild){
		root->rchild->layer = root->layer+1;
		cnt[root->rchild->layer] ++;
		maxLayer = max(maxLayer,root->rchild->layer);
		DFS(root->rchild);
	}
}

柳婼仙女的DFS

void DFS(Node* root,int depth){
	if(root==NULL){
		maxLayer = max(maxLayer,depth);
		return;
	}
	
	cnt[depth] ++;
	DFS(root->lchild,depth+1);
	DFS(root->rchild,depth+1);
}

注意：对左右子结点进行DFS之前不可以判空，否则maxLayer永不会更新！

AC代码

#include<cstdio>
#include<iostream>
#include<set>
#include<vector>
#include<map>
#include<algorithm>
#include<cmath>
#include<queue>

using namespace std;

const int maxn = 1001;

int n;
int cnt[maxn] = {0};
int maxLayer = -1;

struct Node{
	int v;
	Node *lchild,*rchild;
};

void insert(Node* &root,int x){
	if(root==NULL){
		root = new Node;
		root->v = x;
		root->lchild = root->rchild = NULL;
		return;
	}
	
	if(x<=root->v)insert(root->lchild,x);
	if(x>root->v)insert(root->rchild,x);
}

void DFS(Node* root,int depth){
	if(root==NULL){
		maxLayer = max(maxLayer,depth);
		return;
	}
	
	cnt[depth] ++;
	DFS(root->lchild,depth+1);
	DFS(root->rchild,depth+1);
}

int main(){
	
	cin>>n;
	Node* root = NULL;
	for(int i=0;i<n;i++){
		int x;
		cin>>x;
		insert(root,x);
	}

	DFS(root,0);
	
	printf("%d + %d = %d\\n",cnt[maxLayer-1],cnt[maxLayer-2],cnt[maxLayer-1]+cnt[maxLayer-2]);
	
	return 0;
}