[链表]-反转单向和双向链表

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题目：
分别实现反转单向链表和反转双向链表的函数

要求：
如果链表长度为N，时间的复杂度要求为O(N),额外空间的复杂度O(1)

示例代码：

//反转单向链表
public class Node{
public int value;
public Node next;
public Node(int data){
this.value = data;
}
}

public Node reverseList(Node head){
Node pre = null;
Node next = null;
while(head != null){
next = head.next;
head.next = pre;
pre = head;
head = next;
}
return pre;
}

// 反转双向链表
public class DoubleNode{
public int value;
public DoubleNode last;
public DoubleNode next;
public DoubleNode(int data){
this.value = data;
}
}

public DoubleNode reverseList(DoubleNode head){
DoubleNode pre = null;
DoubleNode next = null;
while(head != null){
next = head.next;
head.next = pre;
head.last = next;
pre = head;
head = next;
}
return pre;
}