[LeetCode]Balanced Binary Tree

public class Solution {
boolean result = true;
public boolean isBalanced(TreeNode root) {
helper(root);
return result;
}
public int helper(TreeNode root) {
if (root == null) {
return 0;
}
int left = helper(root.left);
int right = helper(root.right);
if (Math.abs(left - right) > 1) {
result = false;
return -1;
} else {
return Math.max(left, right) + 1;
}
}
}