ReverseNodesInKGroup.java

// https://leetcode.com/problems/reverse-nodes-in-k-group/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 * int val;
 * ListNode next;
 * ListNode() {}
 * ListNode(int val) { this.val = val; }
 * ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
classSolution {
publicListNodereverseKGroup(ListNodehead, intk) {
if (k == 1) returnhead;

ListNodeslow = head, fast = head, newHead = head;
ListNodeprev = null, next = head;
intcount = 0;
booleanisStart = true;

while (fast != null) {
count++;

if (count != k) fast = fast.next;
else {
if (!isStart) {
next = slow.next;
slow.next = fast;
slow = next;
 } else {
isStart = false;
newHead = fast;
 }

prev = fast.next;
ListNodetempFast = fast.next, tempSlow = slow;
while (count > 0) {
count--;
next = slow.next;
slow.next = prev;
prev = slow;
slow = next;
 }
slow = tempSlow;
fast = tempFast;
 }
 }

returnnewHead;
 }
}