Description:

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.

My code:

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function(root) {
    // function depth(layer, tree) 判断是否为null, 不是的话递归调用depth(), 记录父节点的左右节点，比较左右节点的深度，返回较大的
    if(root == null) {
        return 0;
    }
    let left = maxDepth(root.left);
    let right = maxDepth(root.right);
    if(left >= right) {
        return ++left;
    } else {
        return ++right;
    }
};