division_sum_pair.js

// boiler plate for js 
'use strict';

const fs = require('fs');

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', function(inputStdin) {
    inputString += inputStdin;
});

process.stdin.on('end', function() {
    inputString = inputString.split('\n');

    main();
});

function readLine() {
    return inputString[currentLine++];
}

/*
 * Complete the 'divisibleSumPairs' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. INTEGER k
 *  3. INTEGER_ARRAY ar
 */

// actual code
function divisibleSumPairs(n, k, ar) {
    // Write your code here
let count=0
for(let i=0;i<n;i++){
  for(let j=i+1;j<n;j++){
    // checking two diff element sum is divisible by k and if yes then increment the count 
    if((ar[i]+ar[j])%k==0){
      count++
    }
  }
}
return count
}

function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

    const firstMultipleInput = readLine().replace(/\s+$/g, '').split(' ');

    const n = parseInt(firstMultipleInput[0], 10);

    const k = parseInt(firstMultipleInput[1], 10);

    const ar = readLine().replace(/\s+$/g, '').split(' ').map(arTemp => parseInt(arTemp, 10));

    const result = divisibleSumPairs(n, k, ar);

    ws.write(result + '\n');

    ws.end();
}