104. Maximum Depth of Binary Tree

Problem

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.

Solution

/**
 * 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) {
  return helper(root, 0);
};

var helper = function (root, level) {
  if (!root) return level;
  return Math.max(helper(root.left, level + 1), helper(root.right, level + 1));
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(1).