Kotlin: 206. Reverse Linked List

kotlin/206-Reverse-Linked-List.kt

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+/**
+ * Example:
+ * var li = ListNode(5)
+ * var v = li.`val`
+ * Definition for singly-linked list.
+ * class ListNode(var `val`: Int) {
+ * var next: ListNode? = null
+ * }
+ */
+class Solution {
+ fun reverseList(head: ListNode?): ListNode? {
+ if (head == null)
+ return head
+
+ var prev: ListNode? = null
+ var curr = head
+
+ while (curr != null) {
+ val next = curr.next
+ curr.next = prev
+ prev = curr
+ curr = next
+ }
+
+ return prev
+ }
+
+ fun reverseListRecursive(head: ListNode?): ListNode? {
+ if (head == null || head.next == null)
+ return head
+
+ val newHead = reverseList(head.next)
+ head.next.next = head
+ head.next = null
+
+ return newHead
+ }
+}