Add 143_Reorder_List.java

Author: Sean Prashad

In-place Reveral of a Linked List/143_Reorder_List.java

@@ -0,0 +1,41 @@
+class Solution {
+ public void reorderList(ListNode head) {
+ if (head == null) {
+ return;
+ }
+
+ ListNode slow = head, fast = head;
+
+ while (fast.next != null && fast.next.next != null) {
+ slow = slow.next;
+ fast = fast.next.next;
+ }
+
+ ListNode head2 = reverse(slow.next);
+ slow.next = null;
+
+ while (head != null && head2 != null) {
+ ListNode t1 = head.next;
+ ListNode t2 = head2.next;
+
+ head.next = head2;
+ head2.next = t1;
+
+ head = t1;
+ head2 = t2;
+ }
+ }
+
+ private ListNode reverse(ListNode head) {
+ ListNode prev = null, curr = head;
+
+ while (curr != null) {
+ ListNode tmp = curr.next;
+ curr.next = prev;
+ prev = curr;
+ curr = tmp;
+ }
+
+ return prev;
+ }
+}