1721. Swapping Nodes in a Linked List

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題目敘述

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]

解題思路

Solution

// 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; }
}
 

class Solution {
    public ListNode swapNodes(ListNode head, int k) {
        ListNode start = head, end = head;
        
        for (int i = 1; i < k; i++) {
            start = start.next;
        }
        
        ListNode curr = start;
        while (curr.next != null) {
            curr = curr.next;
            end = end.next;
        }
        
        int temp = start.val;
        start.val = end.val;
        end.val = temp;
        
        return head;
    }
}