JSFiddle - React, Tailwind, and code Playground

by garmashnikolay

JavaScript

const a = [4,5,4,8,4,5,4,5,5]

const {sum} =  a.reduce(({sumMap, sum}, number) => {
	const increment = sumMap[number] ? -number : +number
	
  sumMap[number] = !sumMap[number]
  sum += increment
  
	return {sumMap, sum}
}, {sumMap: {}, sum: 0})

console.log(sum)