Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 4

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]

Constraints:

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

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
  int listLength(ListNode *head) {
    int len = 0;
    while(head) {
      len += 1;
      head = head->next;
    }
    return len;
  }
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;
  }
};

// Accepted
// 132/132 cases passed (548 ms)
// Your runtime beats 99.93 % of cpp submissions
// Your memory usage beats 15.97 % of cpp submissions (180.3 MB)