Daily Coding Problem: Problem #622

/**
 * Good morning! Here's your coding interview problem for today.
This problem was asked by Google. Given the root of a binary tree, return a deepest node.
 * */
class TreeNode(var value: Int) {
    var left: TreeNode? = null
    var right: TreeNode? = null
}

class Problem_622 {
    /*
    * soluton DFS: 1. find the height of the tree, 2.scan level by level;
    * Time complexity:O(n), Space complexity:O(1)
    * */
    var deepest = 0

    fun findDeepest(root: TreeNode?): Int {
        if (root == null) {
            return 0
        }
        val level = getHeight(root)
        findDeepest(root, level)
        return deepest
    }

    private fun findDeepest(root: TreeNode?, level: Int) {
        if (root != null) {
            if (level == 1) {
                deepest = root.value
            } else if (level > 1) {
                findDeepest(root.left, level - 1)
                findDeepest(root.right, level - 1)
            }
        }
    }

    private fun getHeight(root: TreeNode?): Int {
        if (root == null) {
            return 0
        }
        val leftHeight = getHeight(root.left)
        val rightHeight = getHeight(root.right)
        return Math.max(leftHeight, rightHeight) + 1
    }
}