[Leetcode 206, Easy] Reverse Linked List

Problem:

Reverse a singly linked list.

Analysis:

Solutions:

C++:

    ListNode* reverseList(ListNode* head) {
        if(head == NULL || head->next == NULL)
            return head;
            
        ListNode *new_head = NULL;
        while(head != NULL) {
            ListNode *temp_old_head = head->next;
            if(new_head == NULL) {
                new_head = head;
                head->next = NULL;
            } else {
                ListNode *temp_new_head = new_head;
                new_head = head;
                new_head->next = temp_new_head;
            }
            head = temp_old_head;
        }
        
        return new_head;
    }

Java:

Python: