add solution of problem 328: Odd Even Linked List

Author: ppulse

OddEvenLinkedList328/README.md

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+Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.
+
+You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.
+
+#####Example:
+Given `1->2->3->4->5->NULL`,
+
+return `1->3->5->2->4->NULL`.
+
+#####Note:
+The relative order inside both the even and odd groups should remain as it was in the input.
+ 
+The first node is considered odd, the second node even and so on ...

OddEvenLinkedList328/Solution.java

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+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public ListNode oddEvenList(ListNode head) {
+        if (head == null)
+            return null;
+        
+        ListNode newHead = head;
+        ListNode currOdd = head;
+        ListNode currEven = head.next;
+        ListNode evenHead = currEven;
+        
+        while (currEven != null) {
+            if (currOdd.next == null || currOdd.next.next == null)
+                currOdd.next = evenHead;
+            else
+                currOdd.next = currOdd.next.next;
+            
+            if (currEven.next != null)
+                currEven.next = currEven.next.next;
+            
+            currOdd = currOdd.next;
+            currEven = currEven.next;
+        }
+        
+        if (currOdd != evenHead)
+            currOdd.next = evenHead;
+        
+        return newHead;
+    }
+}