1128. Number of Equivalent Domino Pairs

class Solution {
    public int numEquivDominoPairs(int[][] dominoes) 
    {

        int result = 0;
        int[][] pairs = new int[9][9];
        
        for(int[] dom: dominoes) 
        {
            pairs[dom[0] - 1][dom[1] - 1]++;
        }

        for(int i = 0; i < 9; i++) 
        {
            for(int j = i; j < 9; j++) 
            {
                int count = pairs[i][j];
                if(i != j) 
                {
                    count += pairs[j][i];
                }

                result += (count * (count - 1)) / 2;
            }
        }

        return result;




        /*


        int result = 0;
        HashMap<Integer, Integer> count = new HashMap<>();

        for(int[] dom : dominoes) 
        {
            int key = Math.min(dom[0], dom[1]) * 10 + Math.max(dom[0], dom[1]);
            result += count.getOrDefault(key, 0);
            count.merge(key, 1, Integer::sum);
        }

        return result;


        */


        /*


        int n = dominoes.length;
        int i=0, count=0;

        HashMap<String, Integer> map = new HashMap<>();

        while(i < n)
        {
            String temp = "";
            
            if(dominoes[i][0] > dominoes[i][1])
            {
                temp += dominoes[i][1];
                temp += dominoes[i][0];

            }
            else
            {
                temp += dominoes[i][0];
                temp += dominoes[i][1];

            }

            if(map.containsKey(temp))
            {
                count += map.get(temp);

            }

            map.put(temp, map.getOrDefault(temp, 0) + 1);
            i++;

        }
        return count;


        */
        
    }
}