solve recorder list

Author: sora0319

reorder-list/sora0319.java

@@ -0,0 +1,38 @@
+public class Solution {
+    public void reorderList(ListNode head) {
+        if (head == null || head.next == null) return;
+
+        ListNode backward = head;
+        ListNode forward = head;
+        while (forward != null && forward.next != null) {
+            backward = backward.next;
+            forward = forward.next.next;
+        }
+
+        ListNode curr = backward.next;
+        backward.next = null;
+
+        ListNode prev = null;
+        while (curr != null) {
+            ListNode tempNext = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = tempNext;
+        }
+
+        ListNode first = head;
+        ListNode second = prev;
+
+        while (second != null) {
+            ListNode firstNext = first.next;
+            ListNode secondNext = second.next;
+
+            first.next = second;
+            second.next = firstNext;
+
+            first = firstNext;
+            second = secondNext;
+        }
+    }
+}
+