(LeetCode) 206. Reverse Linked List

Reverse Linked List

• Explore : Interview > Top Interveiw Questions > Easy Collection
• 분류 : Linked List
• 난이도 : Easy

Problem

Given the head of a singly linked list, reverse the list, and return the reversed list.

Example 1

Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]

Example 2

Input: head = [1,2]
Output: [2,1]

Example 3

Input: head = []
Output: []

Constraints

• The number of nodes in the list is the range [0, 5000].
• -5000 <= Node.val <= 5000

Solution

Exapnder

/**
 * Example:
 * var li = ListNode(5)
 * var v = li.`val`
 * Definition for singly-linked list.
 * class ListNode(var `val`: Int) {
 *     var next: ListNode? = null
 * }
 */
class Solution {
    fun reverseList(head: ListNode?): ListNode? {
        var reverse: ListNode? = null
        var node = head
        while (node != null) {
            reverse = ListNode(node.`val`).apply {
                next = reverse
            }
            node = node.next
        }
        return reverse
    }
}

Point of Thinking

• 임의의 노드를 생성한 뒤, 뒤에서부터 포인터를 연결해주면 끝