Lintcode: Insert Node in a Binary Search Tree

Given a binary search tree  and a new tree node, insert the node into the tree. You should keep the tree still be a valid binary search tree.

Example
Given binary search tree as follow:

     2

  /    

1        4

         /   

       3 

after Insert node 6, the tree should be:

     2

  /    

1        4

         /    

       3        6

Challenge
Do it without recursion

Recursion做法：

public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        // write your code here
        if (root == null) return node;
        if (node == null) return root;
        helper(root, node);
        return root;
    }
    
    public void helper(TreeNode root, TreeNode node) {
        if (root.val <= node.val && root.right == null) root.right = node;
        else if (root.val > node.val && root.left == null) root.left = node;
        else if (root.val <= node.val) helper(root.right, node);
        else helper(root.left, node);
    }
}

Iterative做法：

public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        // write your code here
        if (root == null) return node;
        if (node == null) return root;
        TreeNode rootcopy = root;
        while (root != null) {
            if (root.val<=node.val && root.right==null) {
                root.right = node;
                break;
            }
            else if (root.val>node.val && root.left==null) {
                root.left = node;
                break;
            }
            else if(root.val <= node.val) root = root.right;
            else root = root.left;
        }
        return rootcopy;
    }
}