LeetCode: Balanced Binary Tree

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int dfs(TreeNode *root, bool &flag, int cur) {
if (!root || !flag) return cur;
int leftH = dfs(root->left, flag, cur+1);
if (!flag) return cur;
int rightH = dfs(root->right, flag, cur+1);
if (abs(leftH-rightH) <= 1 && flag) flag = true;
else flag = false;
return max(leftH, rightH);
}
bool isBalanced(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (!root) return true;
bool flag = true;
if (abs(dfs(root->left, flag, 0)-dfs(root->right, flag, 0)) <= 1 && flag) return true;
else return false;
}
};

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