SalesbyMatch.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 'sockMerchant' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. INTEGER_ARRAY ar
 */

function sockMerchant(n, ar) {
    // Write your code here
    var pairA=[];
for(var i=0;i<1000;i++){
   pairA[i]=0; 
}

for( i=0;i<ar.length;i++){
    pairA[ar[i]]++;
}
var total=0;
for(i=1;i<pairA.length;i++){
    if(pairA[i]>=2){
       total=total+parseInt(pairA[i]/2); 
    }
}
return total;
}

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

    const n = parseInt(readLine().trim(), 10);

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

    const result = sockMerchant(n, ar);

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

    ws.end();
}