pairInArray.js

// Return the total number of matching pairs of socks that John can sell.

// 9
// 10 20 20 10 10 30 50 10 20

// output
// 3

function sockMerchant(n, ar) {
    let totalPair=0;
    const pairs = new Set();
    for (let i=0; i <= n; i++) {
        if (!pairs.has(ar[i])) {
            pairs.add(ar[i]);
        } else {
            totalPair++;
            pairs.delete(ar[i]);
        }
    }

    return totalPair;
}