226-InvertBinaryTree.kt

/**
 *
 * 226. Invert Binary Tree
 * https://leetcode.com/problems/invert-binary-tree/
 *
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    fun invertTree(root: TreeNode?): TreeNode? {
        if (root == null) {
            return root
        }

        invertTree(root?.right)
        invertTree(root?.left)

        val aux = root?.left
        root.left = root?.right
        root.right = aux

        return root
    }
}