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 (Java)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int maxDepth(TreeNode A) {
        if(A==null) return 0;
        int l = maxDepth(A.left);
        int r = maxDepth(A.right);
        return Math.max(l,r)+1;
    }  
}

Solution (Javascript)

/**
 * 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).