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

Given binary tree A={3,9,20,#,#,15,7}, B={3,#,20,15,7}

A)  3            B)    3
    / \                  \
  9  20                 20
    /  \                / \
    15   7              15  7

The binary tree A is a height-balanced binary tree, but B is not.