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_206.java
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package com.fishercoder.solutions;
import com.fishercoder.common.classes.ListNode;
/**
* 206. Reverse Linked List
*
* Reverse a singly linked list.
*
* Example:
* Input: 1->2->3->4->5->NULL
* Output: 5->4->3->2->1->NULL
*
* Follow up:
* A linked list can be reversed either iteratively or recursively. Could you implement both?
* */
public class _206 {
public static class Solution1 {
public ListNode reverseList(ListNode head) {
ListNode prev = null;
ListNode curr = head;
while (curr != null) {
ListNode next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
}
public static class Solution2 {
public ListNode reverseList(ListNode head) {
return reverse(head, null);
}
ListNode reverse(ListNode head, ListNode newHead) {
if (head == null) {
return newHead;
}
ListNode next = head.next;
head.next = newHead;
newHead = head;
head = next;
return reverse(head, newHead);
}
}
}