Check sum pair

/* package codechef; // don't place package name! */
import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
public class Main
{
    public static void main (String[] args) throws java.lang.Exception,IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String[] firstLine = br.readLine().split(" ");
        int N = Integer.parseInt(firstLine[0]);
        int K = Integer.parseInt(firstLine[1]);

        String[] numsStr = br.readLine().split(" ");
        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = Integer.parseInt(numsStr[i]);
        }

        getC(K, nums);
    }

    private static void getC(int K, int[] nums) {
        Map<Integer, Integer> map = new HashMap<>();


        int count = 0;

        for (int num : nums) {
            int complement = K - num;

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

            map.put(num, map.getOrDefault(num, 0) + 1);
        }
        System.out.println(count);
    }
}

//test case 10 failed.