Q25ReverseNodes

Q25ReverseNodes.cpp

/**
 * 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==NULL||k==1) return head;
        
        ListNode* p0=head;
        ListNode* p1=head;
        int steps=1;
        while(steps!=k&&p1!=NULL){
            p1=p1->next;
            steps++;
        }
        if(steps!=k||p1==NULL)
            return head;
        ListNode* nextHead=p1->next;
        ListNode* p01=p0->next;
        ListNode* p011;
        while(p0!=p1){
            p011=p01->next;
            p01->next=p0;
            p0=p01;
            p01=p011;
        }
        head->next=reverseKGroup(nextHead, k);
        return p1;
    }
};