题解 | 二叉排序树

#include <bits/stdc++.h>
using namespace std;
typedef struct TreeNode {
	int data;
	struct TreeNode *left, *right;
};
void insertBST(TreeNode* &root,int data,TreeNode* preNode) {
//	cout<<"进入insertBST"<<endl; 
//	cout<<"root="<<root<<endl;
	if(root == NULL) {
//		cout<<"111"<<endl;
		root = (TreeNode*)malloc(sizeof(TreeNode));
		root->data = data;
		root->left = NULL;
		root->right=NULL;
//		cout<<"data="<<data<<endl;
		if(preNode == NULL) {
			cout<<"-1"<<endl;
		} else {
			cout<<preNode->data<<endl;
		}
	} else if(root->data < data) {
//		cout<<"222"<<endl;
		insertBST(root->right,data,root);
	} else {
//		cout<<"333"<<endl;
		insertBST(root->left,data,root);
	}
}
int main() {
	int n = 0;
	cin>>n;
	TreeNode *root = NULL;
	for(int i = 0 ; i < n; i++) {
		int input = 0;
		cin>>input;
		insertBST(root,input,NULL);
	}
	return 0;
}

1、root传 空指针的话一定要初始化为NULL