LeetNode 题解之Reverse Nodes in k-Group

1、题目描述

2、问题分析

这个题本质上还是按照链表翻转的思路来解，只是需要添加一些细节判断。

3、代码

class Solution {
public:
    ListNode* reverseKGroup(ListNode* head, int k) {
        if( !head || head->next == NULL || k <= 1 ){
            return head ;
        }
        
        ListNode dummy(0) ;
        ListNode* d = &dummy ;
        ListNode* p = head ;
      
        while( p != NULL ){
            ListNode* pm = p;
            int n = 1;
            ListNode* nextNode ;
            while( pm != NULL && n < k ){
                pm = pm->next ;
                ++n;
            }
            if( pm != NULL ){
                nextNode = pm->next;
                pm->next = NULL ;
                
                d->next = reverseList( p );
                d = p;
                p = nextNode ;     // k % number of nodes == 0 ,out of while ;
                
            }else{
                d->next = p;
                break; 
            }
            
        }
        
        return dummy.next ;
        
    }
    
    ListNode* reverseList( ListNode* head  ){
        if( !head || head->next == NULL ){
            return head;
        }
        ListNode* p = head ;
        ListNode* q = head->next ;
        head->next = NULL ;
        while( p != NULL && q != NULL ){
            ListNode* tmp = q->next ;
            q->next = p;
            p = q ;
            q = tmp ;
        }
        return p ;
        
    }
};