Count number of pairs

by 420

JavaScript

const a = [20, 20, 30, 10, 10, 30, 50, 10, 20, 20];

const socks = {};
let pair = 0;

a.forEach(item => {
  socks[item] = socks[item] +1 || 1
  if(socks[item] % 2 === 0) {
    pair = pair + 1
  }
})



console.log(pair)