What's the difference between "NULL" and "null" in LeetCode?

• If the input is [1,2,2,3,NULL,NULL,3,4,NULL,NULL,4],the answer is true;
but if the input is [1,2,2,3,null,null,3,4,null,null,4],the answer becomes false.
Why the same input provides different results?

• "Why the same input provides different results?"

Well they're not the same input.

And you can try printing the tree to see that the "NULL" version confuses the parser:

``````bool isBalanced(TreeNode* root) {
queue<TreeNode*> q;
q.push(root);
while (q.size()) {
auto node = q.front();
q.pop();
if (node) {
cout << node->val << ",";
q.push(node->left);
q.push(node->right);
} else {
cout << "null,";
}
}
return true;
}
``````

For [1,2,2,3,null,null,3,4,null,null,4] this prints:

1,2,2,3,null,null,3,4,null,null,4,null,null,null,null,

For [1,2,2,3,NULL,NULL,3,4,NULL,NULL,4] this prints:

1,2,2,3,0,0,3,4,0,0,4,null,null,null,null,null,null,null,null,null,null,null,null,

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