Balanced Binary Tree

/**
 * 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 {
    boolean balance;
    public boolean isBalanced(TreeNode root) {
       balance = true;
       helper(root);
       return balance;
    }

    int helper(TreeNode root) {
        if(root==null)
            return 0;
        int left = helper(root.left);
        int right = helper(root.right);
        if(Math.abs(right-left) > 1)
            balance = false; 
        return Math.max(left, right) + 1;
    }
}