Balanced Binary Tree

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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
      if(root == null) return true;
      
      if(Math.abs(getHeight(root.left) - getHeight(root.right)) > 1)
        return false;
      return isBalanced(root.left) && isBalanced(root.right);
    }
    
    
    public int getHeight(TreeNode root){
        if(root == null)
            return 0;
        return Math.max(getHeight(root.left), getHeight(root.right))+1; // Attention +1
         
    }
}
 

Better Solution (CTCI)

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
        if(checkHeight(root) == -1)
            return false;
        else
            return true;
    }
    
    private int checkHeight(TreeNode root){
        if(root == null)
            return 0;
        
        int leftHeight = checkHeight(root.left);
        if(leftHeight == -1)
            return -1;
        
        int rightHeight = checkHeight(root.right);
        if(rightHeight == -1)
            return -1;
        
        if(Math.abs(leftHeight - rightHeight) > 1)
            return -1;
        else
            return Math.max(leftHeight, rightHeight)+1;
    }
}