LeetCode - Arrays - Number of Equivalent Domino Pairs

Given a list of dominoesdominoes[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

 

Constraints:

  • 1 <= dominoes.length <= 40000
  • 1 <= dominoes[i][j] <= 9

 

class Solution {
    public int numEquivDominoPairs(int[][] dominoes) {
        List<List<Integer>> dList = new ArrayList<List<Integer>>();
        Map<List<Integer>,Integer> dmap = new HashMap<List<Integer>,Integer>();
        int counter = 0;
        for(int i=0;i<dominoes.length;i++){
            List<Integer> d = new ArrayList<Integer>();
            d.add(dominoes[i][0]);
            d.add(dominoes[i][1]);
            Collections.sort(d);
            if(dList.contains(d)) {
                dmap.put(d,dmap.getOrDefault(d,0)+1);
            }
            else dList.add(d);
        }
        //System.out.println(dList);
        //System.out.println(dmap);
        for(int i:dmap.values()){
            counter = counter + (i*(i+1)/2);
        }
        return counter;
    }
}

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