Balanced Binary Tree

Description

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 left and right subtrees of every node differ in height by no 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(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
const isBalanced = (root) => {
  const height = (node, currentHeight) => {
    if (!node) {
      return currentHeight
    }
    let leftHeight = currentHeight
    let rightHeight = currentHeight
    if (node.left) {
      leftHeight = height(node.left, currentHeight + 1)
    }
    if (node.right) {
      rightHeight = height(node.right, currentHeight + 1)
    }
    return leftHeight > rightHeight ? leftHeight : rightHeight
  }
  if (!root) {
    return true
  }
  const leftHeight = root.left ? height(root.left, 1) : 0
  const rightHeight = root.right ? height(root.right, 1) : 0
  if (
    (Math.abs(leftHeight - rightHeight) <= 1) && isBalanced(root.left) && isBalanced(root.right)
  ) {
    return true
  }
  return false
}