反转链表
双指针:
class Solution {
public ListNode reverseList(ListNode head) {
ListNode pre = null, cur = head, next = null;
while(cur != null) {
next = cur.next;
cur.next = pre;
pre = cur;
cur = next;
}
return pre;
}
}
递归:
class Solution {
public ListNode reverseList(ListNode head) {
if(head == null || head.next == null) {
return head;
}
ListNode node = reverseList(head.next);
head.next.next = head;
head.next = null;
return node;
}
}