ITMO Algorithms Course: Week 3 Task 1 written on JavaScript

const EdxIo = require('./EdxIo')

const NUMBER_BASE = 512
const NUMBER_BASE_MAX = 511
const NUMBER_BASE_POW = 9
const MAX_NUM_LENGTH = 4

class Week3Task1 {
    run () {
        this.io = new EdxIo()
        this.buildArray()
        this.digitSort()
        this.writeOutput()

        return this.io.close()
    }

    countSort (bufferArr, counters, digit) {
        counters.fill(0)

        const itemShift = NUMBER_BASE_POW * digit
        for (let i = 0; i < this.arr.length; i++) {
            counters[(this.arr[i] >> itemShift) & NUMBER_BASE_MAX]++
        }

        let prevCounters = counters[0]
        for (let i = 1; i < NUMBER_BASE; i++) {
            if (counters[i] > 0) {
                counters[i] += prevCounters
                prevCounters = counters[i]
            }
        }

        for (let i = this.arr.length - 1; i >= 0; i--) {
            const value = this.arr[i]
            bufferArr[--counters[(value >> itemShift) & NUMBER_BASE_MAX]] = value
        }
    }

    digitSort () {
        let bufferArr = new Uint32Array(this.arr.length)
        const counters = new Uint16Array(NUMBER_BASE)
        for (let digit = 0; digit < MAX_NUM_LENGTH; digit++) {
            this.countSort(bufferArr, counters, digit)
            const arrTmp = this.arr
            this.arr = bufferArr
            bufferArr = arrTmp
        }
    }

    writeOutput () {
        let tenthSum = 0
        for (let i = 0; i < this.arr.length; i += 10) {
            tenthSum += this.arr[i]
        }

        this.io.write(tenthSum)
    }

    buildArray () {
        const firstLength = this.io.nextInt()
        const secondLength = this.io.nextInt()

        const firstArr = new Uint32Array(firstLength)
        for (let i = 0; i < firstLength; i++) {
            firstArr[i] = this.io.nextInt()
        }

        this.arr = new Uint32Array(firstLength * secondLength)
        let offset = 0
        let value
        for (let j = 0; j < secondLength; j++) {
            value = this.io.nextInt()
            for (let i = 0; i < firstLength; i++) {
                this.arr[i + offset] = firstArr[i] * value
            }

            offset += firstLength
        }
    }
}

new Week3Task1().run().catch(console.error)