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;
     }
 }