Leetcode/206.ReverseLinkedList.h at master · bluepp/Leetcode · GitHub

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/*
  2015-07-08
  bluepp
  May the force be with me!

  Reverse a singly linked list.
  https://leetcode.com/problems/reverse-linked-list/
*/

/* iteration */
    ListNode* reverseList(ListNode* head) {

        ListNode *pCurr = head, *prev = NULL;
        while (pCurr)
        {
            ListNode *pNext = pCurr->next;

            pCurr->next = prev;

            prev = pCurr;
            pCurr = pNext;
        }

        return prev;

    }

/* 2018/10/26 */
    ListNode* reverseList(ListNode* head) {

        if (!head || !head->next) return head;

        ListNode *p = head;
        head = reverseList(p->next);
        p->next->next = p;
        p->next = NULL;

        return head;
    }


    /* recursion */
       ListNode* reverseList(ListNode* head) {

        reverse(head);

        return head;
    }

    void reverse(ListNode *&head)
    {
        if (!head) return;

        ListNode *rest = head->next;
        if (!rest) return;

        reverse(rest);
        head->next->next = head;
        head->next = NULL;
        head = rest;
    }