TripleSum.java

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;

public class Solution {

    // Complete the triplets function below.
static long triplets(int[] a, int[] b, int[] c) {
      int[] ar = Arrays.stream(a).sorted().distinct().toArray();
      int[] br = Arrays.stream(b).sorted().distinct().toArray();
      int[] cr = Arrays.stream(c).sorted().distinct().toArray();

      long left = 0;
      long right = 0;
      int l = 0;
      int r = 0;
      long sum = 0;

      for(int i=0; i<br.length; i++) {
        while(l<ar.length&&ar[l]<=br[i]) {
          left++;
          l++;
        }
        while(r<cr.length&&cr[r]<=br[i]) {
          right++;
          r++;
        }
        sum += left*right;
      }
        return sum;
    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        String[] lenaLenbLenc = scanner.nextLine().split(" ");

        int lena = Integer.parseInt(lenaLenbLenc[0]);

        int lenb = Integer.parseInt(lenaLenbLenc[1]);

        int lenc = Integer.parseInt(lenaLenbLenc[2]);

        int[] arra = new int[lena];

        String[] arraItems = scanner.nextLine().split(" ");
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int i = 0; i < lena; i++) {
            int arraItem = Integer.parseInt(arraItems[i]);
            arra[i] = arraItem;
        }

        int[] arrb = new int[lenb];

        String[] arrbItems = scanner.nextLine().split(" ");
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int i = 0; i < lenb; i++) {
            int arrbItem = Integer.parseInt(arrbItems[i]);
            arrb[i] = arrbItem;
        }

        int[] arrc = new int[lenc];

        String[] arrcItems = scanner.nextLine().split(" ");
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int i = 0; i < lenc; i++) {
            int arrcItem = Integer.parseInt(arrcItems[i]);
            arrc[i] = arrcItem;
        }

        long ans = triplets(arra, arrb, arrc);

        bufferedWriter.write(String.valueOf(ans));
        bufferedWriter.newLine();

        bufferedWriter.close();

        scanner.close();
    }
}