Leetcode: Reverse Nodes in k-Group，leetcodek-group

Leetcode: Reverse Nodes in k-Group，leetcodek-group

鏈表的倒轉，

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; *//** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:   ListNode* reverseKGroup(ListNode* head, int k){    if(!head || !head->next || k <= 1)        return head;    ListNode* pFirst = head;    ListNode* pBefore = NULL;    ListNode* pKth = pFirst;    while(1) {        int cnt = k -1;        while(cnt && pKth){            pKth = pKth->next;            cnt--;        }        if(cnt > 0 || pKth == NULL) break;        reverse(pBefore,pFirst,pKth);        if(pBefore == NULL)            head = pFirst;        pBefore = pKth;        pFirst = pKth->next;        pKth = pFirst;    }    return head;   }   void reverse(ListNode* pBefore, ListNode*& pFirst, ListNode*& pKth){    ListNode* p = pFirst;    while(p != pKth) {        ListNode* tmp = p->next;        p->next = pKth->next;        pKth->next = p;        p = tmp;    }    ListNode* tmp = pFirst;    pFirst = pKth;    pKth = tmp;      if(pBefore)        pBefore->next = pFirst;   }};