solve 328.odd-even-linked-list

Author: andavid

vscode/328.odd-even-linked-list.java

@@ -0,0 +1,76 @@
+/*
+ * @lc app=leetcode id=328 lang=java
+ *
+ * [328] Odd Even Linked List
+ *
+ * https://leetcode.com/problems/odd-even-linked-list/description/
+ *
+ * algorithms
+ * Medium (48.16%)
+ * Likes:    872
+ * Dislikes: 237
+ * Total Accepted:    162.4K
+ * Total Submissions: 324K
+ * Testcase Example:  '[1,2,3,4,5]'
+ *
+ * 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.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+  public ListNode oddEvenList(ListNode head) {
+    if (head == null || head.next == null) {
+      return head;
+    }
+
+    ListNode odd = head;
+    ListNode even = head.next;
+    ListNode evenHead = head.next;
+
+    while (even != null && even.next != null) {
+      odd.next = odd.next.next;
+      odd = odd.next;
+      even.next = even.next.next;
+      even = even.next;
+    }
+
+    odd.next = evenHead;
+
+    return head;
+  }
+}
+