701. Insert into a Binary Search Tree

https://leetcode.com/problems/insert-into-a-binary-search-tree/

1. Use iteration:

//
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
        TreeNode* insert = new TreeNode(val);
        if(!root){
            return insert;
        }
        TreeNode* curr = root;
        while(curr){
            if(val > curr->val){
                if(curr->right)
                    curr = curr->right;
                else{
                    curr->right = insert;
                    break;
                }
            } else if (val < curr->val){
                if(curr->left)
                    curr = curr->left;
                else{
                    curr->left = insert;
                    break;
                }
            }
        }
        return root;
    }
};

2. Use BST:

//136 ms    48.8 MB    
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
        if(!root){
            return new TreeNode(val);
        }
        if(val > root->val)
            root->right = insertIntoBST(root->right, val);
        else if (val < root->val)
            root->left = insertIntoBST(root->left, val);
        return root;
    }
};