linear-list/linked-list/reverse-linked-list
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2023-12-01
Reverse Linked List
描述
Reverse a singly linked list.
分析
用双指针 p
, q
,不断前进。
解法 1 迭代
// Reverse Linked List
// Time Complexity: O(n), Space Complexity: O(1)
class Solution {
public ListNode reverseList(ListNode head) {
ListNode p = null;
ListNode q = head;
while (q != null) {
ListNode tmp = q.next;
q.next = p;
p = q;
q = tmp;
}
return p;
}
}
解法 2 递归
// Reverse Linked List
// Time Complexity: O(n), Space Complexity: O(n)
public class Solution {
public ListNode reverseList(ListNode head) {
if (head == null || head.next == null) return head;
ListNode newHead = reverseList(head.next);
head.next.next = head;
head.next = null;
return newHead;
}
}