Reorder List

Author: TonyKim9401

reorder-list/TonyKim9401.java

@@ -0,0 +1,34 @@
+// TC: O(n)
+// -> find middle, reverse, merge -> max O(n)
+// SC: O(1)
+class Solution {
+    public void reorderList(ListNode head) {
+        if (head == null || head.next == null) return;
+
+        ListNode slow = head, fast = head;
+        while (fast != null && fast.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+
+        ListNode backSide = null;
+        ListNode curr = slow.next;
+        slow.next = null;
+
+        while (curr != null) {
+            ListNode temp = curr.next;
+            curr.next = backSide;
+            backSide = curr;
+            curr = temp;
+        }
+
+        ListNode first = head;
+        ListNode second = backSide;
+        while (second != null) {
+            ListNode temp = first.next;
+            first.next = second;
+            first = second;
+            second = temp;
+        }
+    }
+}