206 Reverse Linked List
206. Reverse Linked List
1. Question
Reverse a singly linked list.
Hint:
A linked list can be reversed either iteratively or recursively. Could you implement both?
2. Implementation
(1) Iterative
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode reverseList(ListNode head) {
ListNode preNode = null, curNode = head, nextNode = null;
while (curNode != null) {
nextNode = curNode.next;
curNode.next = preNode;
preNode = curNode;
curNode = nextNode;
}
return preNode;
}
}
3. Time & Space Complexity
Iterative: 时间复杂度O(n), 空间复杂度O(1)
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