MaximumDepthOfBinaryTree.kt

/**
 * Given a binary tree, find its maximum depth.
 *
 * The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
 *
 * For example:
 * Given binary tree [3,9,20,null,null,15,7],
 *
 *  3
 * / \
 * 9 20
 *   / \
 *  15 7
 *
 * return its depth = 3.
 *
 * Accepted.
 */

class MaximumDepthOfBinaryTree {

    fun maxDepth(root: TreeNode?): Int {
        val maxDepth = 0
        return if (root != null) {
            Math.max(maxDepth(root.left), maxDepth(root.right)) + 1
        } else maxDepth
    }

    class TreeNode constructor(var `val`: Int) {

        var left: TreeNode? = null
        var right: TreeNode? = null

    }

}