25. Reverse Nodes in k-Group

最新推荐文章于 2020-07-05 15:42:20 发布

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本文介绍了一种链表操作算法——K组翻转。该算法实现了一个功能，即每K个一组翻转链表，并提供了完整的C++代码实现及解析。通过递归方式处理链表节点，实现了链表的有效翻转。

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

class Solution {
public:
    typedef pair<ListNode*,ListNode*> ListNodePair;
    ListNode* reverseKGroup(ListNode* head, int k) {
        if(head == NULL || k == 1) {
            return head;
        }
        ListNode *newHead,*Tail;
        newHead = Tail = NULL;
        while(head != NULL) {
            int num = 0;
            ListNode *tempHead = head,*tempTail = NULL;
            while(head != NULL && num < k) {
                num++;
                tempTail = head;
                head     = head->next;
            }
            tempTail->next = NULL;
            if(num == k) {
                ListNodePair pairList = reverseList(tempHead);
                if(newHead == NULL) {
                    newHead = pairList.first;
                    Tail    = pairList.second;
                } else {
                    Tail->next = pairList.first;
                    Tail       = pairList.second;
                }
            }
            else {
                if(newHead == NULL) {
                    newHead = tempHead;
                } else {
                    Tail->next = tempHead;
                }
            }
        }
        return newHead;
    }
    ListNodePair reverseList(ListNode *head) {
        ListNode *theNext,*underNext,*Tail;
        theNext     = head->next;
        Tail        = head;
        while(theNext != NULL) {
            underNext       = theNext->next;
            theNext->next   = head;
            Tail->next      = underNext;
            head            = theNext;
            theNext         = underNext;
        }
        return make_pair(head,Tail);
    }
};