2023-05-17 Daily Challenge

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In: DailyChallenge

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

May LeetCoding Challenge 17

Description

Maximum Twin Sum of a Linked List

In a linked list of size n, where n is even, the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node, if 0 <= i <= (n / 2) - 1.

  • For example, if n = 4, then node 0 is the twin of node 3, and node 1 is the twin of node 2. These are the only nodes with twins for n = 4.

The twin sum is defined as the sum of a node and its twin.

Given the head of a linked list with even length, return the maximum twin sum of the linked list.

 

Example 1:

Input: head = [5,4,2,1]
Output: 6
Explanation:
Nodes 0 and 1 are the twins of nodes 3 and 2, respectively. All have twin sum = 6.
There are no other nodes with twins in the linked list.
Thus, the maximum twin sum of the linked list is 6.

Example 2:

Input: head = [4,2,2,3]
Output: 7
Explanation:
The nodes with twins present in this linked list are:
- Node 0 is the twin of node 3 having a twin sum of 4 + 3 = 7.
- Node 1 is the twin of node 2 having a twin sum of 2 + 2 = 4.
Thus, the maximum twin sum of the linked list is max(7, 4) = 7.

Example 3:

Input: head = [1,100000]
Output: 100001
Explanation:
There is only one node with a twin in the linked list having twin sum of 1 + 100000 = 100001.

 

Constraints:

  • The number of nodes in the list is an even integer in the range [2, 105].
  • 1 <= Node.val <= 105

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int pairSum(ListNode* head) {
    vector<int> nums;
    while(head) {
      nums.push_back(head->val);
      head = head->next;
    }
    int answer = 0;
    int len = nums.size();
    for(int i = 0; i < len / 2; ++i) {
      answer = max(answer, nums[i] + nums[len - i - 1]);
    }

    return answer;
  }
};

// Accepted
// 46/46 cases passed (200 ms)
// Your runtime beats 99.58 % of cpp submissions
// Your memory usage beats 42.56 % of cpp submissions (126.5 MB)
Algorithm