Invert Binary Tree

Invert a binary tree.

Example:

Input:

     4
   /   \
  2     7
 / \   / \
1   3 6   9

Output:

     4
   /   \
  7     2
 / \   / \
9   6 3   1

Solution

Using recursion.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        invert(root);
        return root;
    }

    public TreeNode invert(TreeNode node) {
        if (node == null) {
            return null;
        }
        TreeNode right = node.right;
        node.right = invert(node.left);
        node.left = invert(right);
        return node;
    }
}