public class ListNode {
int val;
ListNode next;
public ListNode(int val) {
this.val = val;
}
}
1.用迭代的方法反轉(zhuǎn)鏈表(iteratively)
class Solution {
public ListNode reverseList(ListNode head) {
if (head == null) {
return null;
}
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode pre = dummy.next;
ListNode start = pre.next;
ListNode then = start.next;
while (then != null) {
start.next = then.next;
then.next = pre.next;
pre.next = then;
then = start.next;
}
return dummy.next;
}
}
2.用遞歸的方法反轉(zhuǎn)鏈表(recursively)
class Solution {
public ListNode reverseList(ListNode head){
if (head.next == null || head == null) {
return head;
}
ListNode nextNode = head.next;
ListNode last = reverseList(nextNode);
nextNode.next = head;
head.next = null;
return last;
}
}
