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

October LeetCoding Challenge 4

Description

Divide Players Into Teams of Equal Skill

You are given a positive integer array skill of even length n where skill[i] denotes the skill of the ith player. Divide the players into n / 2 teams of size 2 such that the total skill of each team is equal.

The chemistry of a team is equal to the product of the skills of the players on that team.

Return the sum of the chemistry of all the teams, or return -1 if there is no way to divide the players into teams such that the total skill of each team is equal.

Example 1:

Input: skill = [3,2,5,1,3,4]
Output: 22
Explanation: 
Divide the players into the following teams: (1, 5), (2, 4), (3, 3), where each team has a total skill of 6.
The sum of the chemistry of all the teams is: 1 * 5 + 2 * 4 + 3 * 3 = 5 + 8 + 9 = 22.

Example 2:

Input: skill = [3,4]
Output: 12
Explanation: 
The two players form a team with a total skill of 7.
The chemistry of the team is 3 * 4 = 12.

Example 3:

Input: skill = [1,1,2,3]
Output: -1
Explanation: 
There is no way to divide the players into teams such that the total skill of each team is equal.

Constraints:

• 2 <= skill.length <= 105
• skill.length is even.
• 1 <= skill[i] <= 1000

Solution

class Solution {
public:
  long long dividePlayers(vector<int>& skill) {
    map<int, int> count;
    int sum = 0;
    for(auto s : skill) {
      count[s] += 1;
      sum += s;
    }
    int target = sum / (skill.size() / 2);
    if(sum % target) return -1;
    long long answer = 0;
    for(const auto &[s, c] : count) {
      if(s * 2 > target) break;
      if(count[target - s] != c || (s * 2 == target && c % 2)) return -1;
      if(s * 2 != target) {
        answer += 1LL * c * s * (target - s);
      } else {
        answer += 1LL * c / 2 * s * s;
      }
    }
    return answer;
  }
};