Check for Balanced Tree.cpp

/*
Check for Balanced Tree
=======================

Given a binary tree, find if it is height balanced or not. 
A tree is height balanced if difference between heights of left and right subtrees is not more than one for all nodes of tree. 

A height balanced tree
        1
     /     \
   10      39
  /
5

An unbalanced tree
        1
     /    
   10   
  /
5

Example 1:
Input:
      1
    /
   2
    \
     3 
Output: 0
Explanation: The max difference in height
of left subtree and right subtree is 2,
which is greater than 1. Hence unbalanced

Example 2:
Input:
       10
     /   \
    20   30 
  /   \
 40   60
Output: 1
Explanation: The max difference in height
of left subtree and right subtree is 1.
Hence balanced. 
Your Task:
You don't need to take input. Just complete the function isBalanced() that takes root node as parameter and returns true, if the tree is balanced else returns false.

Constraints:
1 <= Number of nodes <= 105
0 <= Data of a node <= 106

Expected time complexity: O(N)
Expected auxiliary space: O(h) , where h = height of tree
*/

bool helper(Node *root, int &height)
{
  if (!root)
  {
    height = 0;
    return true;
  }

  int lh = 0, rh = 0;
  auto left = helper(root->left, lh);
  auto right = helper(root->right, rh);

  height = 1 + max(lh, rh);
  return abs(lh - rh) < 2 && left && right;
}

//Function to check whether a binary tree is balanced or not.
bool isBalanced(Node *root)
{
  if (!root)
    return true;
  int height = 0;
  return helper(root, height);
}