110. Balanced Binary Tree

Problem

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7

Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
  return helper(root, 0) >= 0;
};

var helper = function (root, depth) {
  if (!root) return depth;
  var left = helper(root.left, depth + 1);
  var right = helper(root.right, depth + 1);
  if (left === -1 || right === -1 || Math.abs(left - right) > 1) return -1;
  return Math.max(left, right);
};

Explain:

nope.

Complexity:

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