Lintcode85-Insert Node in a Binary Search Tree-Easy

85. 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

Example 1:
	Input:  tree = {}, node = 1
	Output:  1

	Explanation:
	Insert node 1 into the empty tree, so there is only one node on the tree.

Example 2:
	Input: tree = {2,1,4,3}, node = 6
	Output: {2,1,4,3,6}

	Explanation:
	Like this:

	  2             2
	 / \           / \
	1   4   -->   1   4
	   /             / \
	  3             3   6

Challenge

Can you do it without recursion?

思路：

在树上定位要插入节点的位置。

1. 如果它大于当前根节点，则应该在右子树中，如果没有右子树则将该点作为右儿子插入；若存在右子树则在右子树中继续定位。
2. 如果它小于当前根节点，则应该在左子树中，处理同上。

（二叉查找树中保证不插入已经存在的值）

二分法代码：

public TreeNode insertNode(TreeNode root, TreeNode node) {
        if (root == null) {
            return node;
        }
        if (root.val > node.val) {
            root.left = insertNode(root.left, node);
        } else {
            root.right = insertNode(root.right, node);
        }
        return root;
    }