LeetCode-in-Java

1721. Swapping Nodes in a Linked List

Medium

You are given the head of a linked list, and an integer k.

Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed).

Example 1:

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

Output: [1,4,3,2,5]

Example 2:

Input: head = [7,9,6,6,7,8,3,0,9,5], k = 5

Output: [7,9,6,6,8,7,3,0,9,5]

Constraints:

• The number of nodes in the list is n.
• 1 <= k <= n <= 105
• 0 <= Node.val <= 100

Solution

import com_github_leetcode.ListNode;

/*
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
public class Solution {
    public ListNode swapNodes(ListNode head, int k) {
        ListNode beg = null;
        ListNode end = null;
        ListNode node = head;
        while (node != null) {
            k--;
            if (k == 0) {
                beg = node;
                end = head;
            } else if (end != null) {
                end = end.next;
            }
            node = node.next;
        }
        if (beg != null) {
            int tem = beg.val;
            beg.val = end.val;
            end.val = tem;
        }
        return head;
    }
}

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