package leetCode_25;

/**

* @author dimdark

* @date 2017-10-08

* @time 9:58 PM

*/

public class Solution {

class ListNode {

int val;

ListNode next;

ListNode(int x) {

this.val = x;

}

}

private ListNode reverse(ListNode first, ListNode last) {

ListNode prev = last;

while (first != last) {

ListNode temp = first.next;

first.next = prev;

prev = first;

first = temp;

}

return prev;

}

public ListNode reverseKGroup(ListNode head, int k) {

if (k <= 0) return head;

ListNode node = head;

for (int i = 0; i < k; ++i) {

if (node == null) {

return head;

}

node = node.next;

}

ListNode newHead = reverse(head, node);

head.next = reverseKGroup(node, k);

return newHead;

}

}