LeetCode Balanced Binary Tree

bool isBalancedRecursive(TreeNode *root,int &lenth)
{
if(root==NULL)
{
lenth = 0;
return true;
}
int leftlenth,rightlenth;
if (isBalancedRecursive(root->left,leftlenth)&&isBalancedRecursive(root->right,rightlenth))
{
lenth = leftlenth>rightlenth?leftlenth+1:rightlenth+1;
if(leftlenth-rightlenth<=1&&leftlenth-rightlenth>=-1)
return true;
else
return false;
}
else
return false;
}
bool isBalanced(TreeNode *root) {
if(root==NULL)
return true;
int lenth;
return isBalancedRecursive(root,lenth);
}