samples/2022/03/algorithms/factorial2.js

'use strict';

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();
});

process.on('SIGINT', function() {
    inputString = inputString.split('\n');

    main();
    process.exit(0);
});

function readLine() {
    return inputString[currentLine++];
}

/*
 * Complete the 'extraLongFactorials' function below.
 *
 * The function accepts INTEGER n as parameter.
 */

// the idea to store digits in array
// but the system is 1000 base instead of 10
// just for printing issues

function convert_to(n) {
    let res = [];
    let digit;
    do {
        digit = n % 1000;
        res.unshift(digit);
        n = Math.floor(n / 1000);
    } while (n > 0);
    
    return res;
}

function sum(a, b) {
    let da, db, shift = 0, res;
    let digits = [];
    while (a.length || b.length) {
        da = a.length ? a.pop() : 0;
        db = b.length ? b.pop() : 0;
        res = da + db + shift;
        digits.unshift(res % 1000);
        shift = Math.floor(res / 1000);
    }
    if (shift > 0) {
        digits.unshift(shift);
    }
    return digits;
}

function multiply(a, b) {
    // console.log('multiply', a, b);
    let n = a.length;
    let m = b.length;
    let da, db, shift = 0, res;
    
    let offsetArray = [];
    let subSum;
    let sumAll = [0];
    
    for (let i = m - 1; i >= 0; i--) {
        subSum = [...offsetArray];
        offsetArray.push(0);
        for (let j = n - 1; j >= 0; j--) {
            res = b[i] * a[j] + shift;
            subSum.unshift(res % 1000);
            shift = Math.floor(res / 1000);
        }
        if (shift > 0) {
            subSum.unshift(shift);
        }
        // console.log('Subsum', subSum);
        sumAll = sum(sumAll, subSum);
        // console.log('Summed', sumAll);
    }
    return sumAll;
}

function extraLongFactorials(n) {
    let m = [1];
    let factor = [0];
    for (let i = 0; i < n; i++) {
        factor = sum(factor, [1]);
        console.log(`Factor`, m, factor);
        m = multiply(m, factor);
    }

    console.log(`Result`, m);

    let s = "" + m[0];
    for (let i = 1; i < m.length; i++) {
        s += ("" + m[i]).padStart(3, "0");
    }

    console.log(s);
}

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

    extraLongFactorials(n);
}