Why is this implementation for checking balanced binary tree wrong - data-structures

Question

public boolean isBalanced(TreeNode root) {
if(root == null) return true;
int rightCount = maxDepth(root.right);
int leftCount = maxDepth(root.left);
if(Math.abs(rightCount-leftCount)<=1) return true;
return false;
}
public int maxDepth(TreeNode root){
if(root == null) return 0;
return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
}
Checking the max depth for both branches and determining if the absolute value is <=1

Answer 1

At first:
If you have invalid root arg isBalanced returns true, so that is bad implementation, despite the fact that code could have no errors.
In my opinion, function should work with valid arguments, otherwise throw exception (error?).
Also check this solution, read code and try to do something like this:
/* C program to check if a tree is height-balanced or not */
#include <stdio.h>
#include <stdlib.h>
#define bool int
/* A binary tree node has data, pointer to left child
and a pointer to right child */
struct node {
int data;
struct node* left;
struct node* right;
};
/* Returns the height of a binary tree */
int height(struct node* node);
/* Returns true if binary tree with root as root is height-balanced */
bool isBalanced(struct node* root)
{
int lh; /* for height of left subtree */
int rh; /* for height of right subtree */
/* If tree is empty then return true */
if (root == NULL)
return 1;
/* Get the height of left and right sub trees */
lh = height(root->left);
rh = height(root->right);
if (abs(lh - rh) <= 1 && isBalanced(root->left) && isBalanced(root->right))
return 1;
/* If we reach here then tree is not height-balanced */
return 0;
}
/* UTILITY FUNCTIONS TO TEST isBalanced() FUNCTION */
/* returns maximum of two integers */
int max(int a, int b)
{
return (a >= b) ? a : b;
}
/* The function Compute the "height" of a tree. Height is the
number of nodes along the longest path from the root node
down to the farthest leaf node.*/
int height(struct node* node)
{
/* base case tree is empty */
if (node == NULL)
return 0;
/* If tree is not empty then height = 1 + max of left
height and right heights */
return 1 + max(height(node->left), height(node->right));
}
/* Helper function that allocates a new node with the
given data and NULL left and right pointers. */
struct node* newNode(int data)
{
struct node* node = (struct node*)
malloc(sizeof(struct node));
node->data = data;
node->left = NULL;
node->right = NULL;
return (node);
}
int main()
{
struct node* root = newNode(1);
root->left = newNode(2);
root->right = newNode(3);
root->left->left = newNode(4);
root->left->right = newNode(5);
root->left->left->left = newNode(8);
if (isBalanced(root))
printf("Tree is balanced");
else
printf("Tree is not balanced");
getchar();
return 0;
}
(copy & pasted from here)