class Solution {
public:
    bool isBalanced(TreeNode* root) 
    {
        if (NULL == root)
        {
            return true;
        }
        int ld = getBinaryDepth(root->left);
        int rd = getBinaryDepth(root->right);
        if (ld-rd>1 || rd-ld>1)
        {
            return false;
        }
        else
        {
            return isBalanced(root->left) && isBalanced(root->right);
        }
    }
private:
    int getBinaryDepth(TreeNode* root)
    {
        if (NULL == root)
        {
            return 0;
        }
        int ld = 1 + getBinaryDepth(root->left);
        int rd = 1 + getBinaryDepth(root->right);
        return ld > rd ? ld : rd;
    }
};