Bug Report for Memory Consumption

[mariopavlov]

Bug Report for https://neetcode.io/problems/reverse-a-linked-list

Please describe the bug below and include any steps to reproduce the bug or screenshots if possible.

Having the following solution on my end:

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
		ListNode* prev = nullptr;
		auto cur = head;

		while (cur) {
			auto temp = cur->next;

			cur->next = prev;

			prev = cur;
			cur = temp;
		}

		return prev;
    }
};

I have received 148 MBs from the grading system. Here is the exact report:

Memory: 148.1 MB
Time: 2ms

Submitted at: 02/27/2026 17:09

Then I saw that there are better submissions in terms of memory allocation, and I checked the code:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(!head || !head->next)return head;

        ListNode* prev=NULL;
        ListNode* node=head;

        while(node!=NULL){
            ListNode* front=node->next;
            node->next=prev;
            prev=node;
            node=front;
        }
        // head=node;
        return prev;
    }
};

For that submission we have the following: Runtime: 2ms Memory: 1.1 MB.

How is it possible that similar solutions have such big difference in Memory allocation? Given that I use auto, which is compiler feature? Am I missing something here, or there is a bug in the grading and measuring process?