链表

剑指 Offer 06. 从尾到头打印链表

输入一个链表的头节点，从尾到头反过来返回每个节点的值（用数组返回）。

示例 1：

输入：head = [1,3,2]
输出：[2,3,1]

限制：

0 <= 链表长度 <= 10000

//递归
func reversePrint(head *ListNode) []int {
    if head == nil {
        return nil
    }

    return append(reversePrint(head.Next), head.Val)
}

//栈
func reversePrint(head *ListNode) []int {

    if head == nil {
        return nil
    }

    var pre *ListNode
    for head != nil {
        temp := head.Next
        head.Next = pre
        pre = head
        head = temp
    }

    var res []int
    for pre != nil {
        res = append(res, pre.Val)
        pre = pre.Next
    }
    return res
}

剑指 Offer 24. 反转链表

定义一个函数，输入一个链表的头节点，反转该链表并输出反转后链表的头节点。

示例:

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

限制：

0 <= 节点个数 <= 5000

//栈
func reverseList(head *ListNode) *ListNode {
    if head == nil || head.Next == nil {
        return head
    }

    var newhead *ListNode
    for head != nil {
        temp := head.Next
        head.Next = newhead
        newhead = head
        head = temp
    }

    return newhead
}

//递归
func reverseList(head *ListNode) *ListNode {
    if head == nil || head.Next == nil {
        return head
    }

    newHead := reverseList(head.Next)
    head.Next.Next = head
    head.Next = nil
    return newHead
}