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public class ReverseNodesInKGroup {
public ListNode reverseKGroup(ListNode head, int k) {
if (head == null || head.next == null) {
return head;
}
int length = 0;
ListNode pre = head;
while (pre != null) {
length++;
pre = pre.next;
}
if (k > length) {
return head;
}
int count = length / k;
if (k == 1 || count < 1) {
return head;
}
ListNode preHead = new ListNode(0);
preHead.next = head;
pre = preHead;
ListNode cursor = head;
List<ListNode> list = new ArrayList<ListNode>(k);
while (count > 0) {
list.clear();
for (int i = 0; i < k; i++) {
list.add(cursor);
cursor = cursor.next;
if (i > 0) {
list.get(i).next = list.get(i - 1);
}
}
list.get(0).next = cursor;
pre.next = list.get(k - 1);
pre = list.get(0);
count--;
}
return preHead.next;
}
@Test
public void test() {
ListNode l = new ListNode(1);
l.next = new ListNode(2);
l.next.next = new ListNode(3);
l.next.next.next = new ListNode(4);
l.next.next.next.next = new ListNode(5);
ListNode result = reverseKGroup(l, 5);
}
}
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