左程云_算法与数据结构 — 链表问题 — 04反转单向和双向链表

问题描述

思路分析

代码实现

package algorithm_zuochengyun;

// 给定一个单向链表头结点head,将链表反转
public static Node reverseList(Node head) {
Node pre = null;
Node next = null;
if (head == null || head.next == null) {
return head;
}
while (head != null) {
next = head.next;
head.next = pre;
pre = head;
head = next;
}
return pre;
}

public static Node getReverseListFirst(Node head, int n) {
// 假设123456789 从1翻转到5即可得 543216789
// 此方法返回5这个结点，node(1).next = null;
Node pre = null;
Node next = null;
if (head == null || head.next == null) {
return head;
}
while (n-- > 0) {
next = head.next;
head.next = pre;
pre = head;
head = next;
}
return pre;
}

public static Node getReverseListRest_First(Node head, int n) {
// 假设123456789 从1翻转到5即可得 543216789
// 此方法返回6这个结点
Node pre = null;
Node next = null;
if (head == null || head.next == null) {
return head;
}
while (n-- > 0) {
next = head.next;
head.next = pre;
pre = head;
head = next;
}
return next;
}

public static DoubleNode reverseList(DoubleNode head) {
if (head == null || head.next == null) {
return head;
}
DoubleNode last = null;
DoubleNode next = null;
DoubleNode cur = head;
DoubleNode temp = null;
while (cur != null) {
next = cur.next;
cur.next = last;
last = cur.last;
cur.last = next;
last = cur;
cur = next;

}
return last;
}

public static void main(String[] args) {
Node head = Node.init();
Node.Print(head);
// Node.Print(reverseList(head));
Node.Print(getReverseListFirst(head, 7));

DoubleNode head1 = DoubleNode.init();
DoubleNode.PrintNext(head1);
DoubleNode.PrintNext(reverseList(head1));

}

实现结果

问题总结