104.maximum-depth-of-binary-tree.kt

/*
 * @lc app=leetcode id=104 lang=kotlin
 *
 * [104] Maximum Depth of Binary Tree
 *
 * https://leetcode.com/problems/maximum-depth-of-binary-tree/description/
 *
 * algorithms
 * Easy (59.52%)
 * Total Accepted:    480.4K
 * Total Submissions: 802.8K
 * Testcase Example:  '[3,9,20,null,null,15,7]'
 *
 * 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.
 * 
 * Note: A leaf is a node with no children.
 * 
 * Example:
 * 
 * Given binary tree [3,9,20,null,null,15,7],
 * 
 * 
 * ⁠   3
 * ⁠  / \
 * ⁠ 9  20
 * ⁠   /  \
 * ⁠  15   7
 * 
 * return its depth = 3.
 * 
 */
/**
 * 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 {
    var res = 0
    fun maxDepth(root: TreeNode?): Int {
        if (root == null) return 0

        val left = maxDepth(root.left)
        val right = maxDepth(root.right)

        return if (left >= right) left+1 else right+1
    }
}