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

May LeetCoding Challenge 4

Description

Number of Equivalent Domino Pairs

Given a list of dominoes, dominoes[i] = [a, b] is equivalent to dominoes[j] = [c, d] if and only if either (a == c and b == d), or (a == d and b == c) - that is, one domino can be rotated to be equal to another domino.

Return the number of pairs (i, j) for which 0 <= i < j < dominoes.length, and dominoes[i] is equivalent to dominoes[j].

Example 1:

Input: dominoes = [[1,2],[2,1],[3,4],[5,6]]
Output: 1

Example 2:

Input: dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]
Output: 3

Constraints:

• 1 <= dominoes.length <= 4 * 104
• dominoes[i].length == 2
• 1 <= dominoes[i][j] <= 9

Solution

class Solution {
public:
  int numEquivDominoPairs(vector<vector<int>>& dominoes) {
    map<int, int> count;
    for(auto &domino : dominoes) {
      if(domino[0] < domino[1]) {
        count[domino[0] * 10 + domino[1]] += 1;
      } else {
        count[domino[1] * 10 + domino[0]] += 1;
      }
    }
    int answer = 0;
    for(auto [_code, c] : count) {
      answer += c * (c - 1) / 2;
    }
    return answer;
  }
};

// Accepted
// 19/19 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 32.75 % of cpp submissions (26.4 MB)