Today is Sunday, I gonna review the tasks I've done this week, and finish today's leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 14

Description

Swapping Nodes in a Linked List

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]

Example 3:

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

Example 4:

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

Example 5:

Input: head = [1,2,3], k = 2
Output: [1,2,3]

Constraints:

• The number of nodes in the list is n.
• $1 \le k \le n \le 10^5$
• 0 <= Node.val <= 100

Solution

int listLength(ListNode *head) {
  int len = 0;
  while(head) {
    len += 1;
    head = head->next;
  }
  return len;
}
class Solution {
public:
  ListNode* swapNodes(ListNode* head, int k) {
    int len = listLength(head);
    int first = k - 1;
    int second = len - k;
    ListNode *nodeFirst = head;
    while(first--) nodeFirst = nodeFirst->next;
    ListNode *nodeSecond = head;
    while(second--) nodeSecond = nodeSecond->next;
    swap(nodeFirst->val, nodeSecond->val);
    return head;
  }
};