Odd even LL

Author: Narahari-Sundaragopalan

exercises/leetcode/oddEvenLinkedList.js

@@ -0,0 +1,52 @@
+/**
+ * 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 1:
+
+Input: 1->2->3->4->5->NULL
+Output: 1->3->5->2->4->NULL
+Example 2:
+
+Input: 2->1->3->5->6->4->7->NULL
+Output: 2->3->6->7->1->5->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 ...
+ */
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+const oddEvenLinkedList = head => {
+
+    if (!head) {
+        return null;
+    }
+
+    let odd = head;
+    let even = head.next;
+    let evenHead = even;
+
+    while (even !== null && even.next !== null) {
+        odd.next = even.next;
+        odd = odd.next;
+        even.next = odd.next;
+        even = even.next;
+    }
+
+    odd.next = evenHead;
+    return head;
+}