BalancedBinaryTree.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
        if(root==null){
            return true;
        }
        if(root.left==null && root.right==null) return true;
        
        if(isBalanced(root.left) && isBalanced(root.right)){
            int lHeight=height(root.left);
            int rHeight=height(root.right);
            if(lHeight-rHeight>=-1 && lHeight-rHeight<=1){
                return true;
            }
        }
        return false;
    }
    
    private int height(TreeNode root){
        if(root==null){
            return -1;
        }
        
        return Math.max(height(root.left),height(root.right))+1;
    }
}