Insert Node in a Binary Search Tree

题目：

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.

分析：

iterative的解法需要记得，insert总是发生在leaf上面，于是可以这么做，都第二遍了，还不会

解法iterative：

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;
        }
        TreeNode curr = root;
        TreeNode prev = null;
        while (curr != null) {
            prev = curr;
            if (node.val < curr.val) {
                curr = curr.left;
            } else {
                curr = curr.right;
            }
        }
        if (node.val < prev.val) {
            prev.left = node;
        } else {
            prev.right = node;
        }
        return root;
    }
}

解法recursion：

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.val < root.val) {
            root.left = insertNode(root.left, node);
        } else {
            root.right = insertNode(root.right, node);
        }

        return root;
    }
}