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/**
* 反转链表
* <p>
* 想要链表反转时不断裂,至少需要3个变量记录,pre,cur,post。
* 与前面的题目类似,初始化pre为null,cur为head,post为head.next。
* 初始化之前要注意检查链表的长度。
*
* @author VicterTian
* @version V1.0
* @Date 2019/2/25
*/
public class P142_ReverseList {
static class ListNode<T> {
T val;
ListNode<T> next;
ListNode(T val) {
this.next = null;
this.val = val;
}
@SuppressWarnings("all")
@Override
public String toString() {
StringBuilder ret = new StringBuilder();
ret.append("[");
for (ListNode cur = this; ; cur = cur.next) {
if (cur == null) {
ret.deleteCharAt(ret.lastIndexOf(" "));
ret.deleteCharAt(ret.lastIndexOf(","));
break;
}
ret.append(cur.val);
ret.append(", ");
}
ret.append("]");
return ret.toString();
}
}
private static ListNode reverseList(ListNode head) {
if (head == null ) {
return null;
}
// 说明两边搜长度为一,可以直接返回它本身
if (head.next == null){
return head;
}
ListNode pre = null;
ListNode cur = head;
ListNode post = head.next;
while (true) {
cur.next = pre;
pre = cur;
cur = post;
if (post != null) {
post = post.next;
} else {
return pre;
}
}
}
public static void main(String[] args){
ListNode<Integer> head = new ListNode<>(1);
/* head.next= new ListNode<>(2);
head.next.next = new ListNode<>(3);*/
System.out.println(head);
head = reverseList(head);
System.out.println(head);
}
}