Example: factorial

Factorial with memoization.

import { Decimal, DecimalConstants, MathContext } from '@phensley/cldr';

type Cache = { [x: number]: Decimal };

class Factorial {

  private cache: Cache = { 1: DecimalConstants.ONE };

  constructor(private mc: MathContext) {}

  calculate(n: number): Decimal {
    let r = this.cache[n];
    if (r) {
      return r;
    }
    r = new Decimal(n);
    if (n > 2) {
      r = r.multiply(this.calculate(n - 1), this.mc);
    }
    this.cache[n] = r;
    return r;
  }
}

const reverse = (s: string) =>
  s.split('').reverse().join('');

const spacer = (s: string): string =>
  s.replace(/\w{5}|\w+/g, (m) => ` ${m}`).trim();

const fac = new Factorial({ precision: 100 });
const results: [number, string][] = [];
let width = 0;

for (let n = 1; n <= 50; n++) {
  const tmp = fac.calculate(n).toString();
  const result = reverse(spacer(reverse(tmp)));
  width = Math.max(result.length, width);
  results.push([n, result]);
}

for (const result of results) {
  const [ n, s ] = result;
  log(`${' '.repeat(width - s.length)}${s} = ${n}!`);
}

                                                                            1 = 1!
                                                                            2 = 2!
                                                                            6 = 3!
                                                                           24 = 4!
                                                                          120 = 5!
                                                                          720 = 6!
                                                                         5040 = 7!
                                                                        40320 = 8!
                                                                      3 62880 = 9!
                                                                     36 28800 = 10!
                                                                    399 16800 = 11!
                                                                   4790 01600 = 12!
                                                                  62270 20800 = 13!
                                                                8 71782 91200 = 14!
                                                              130 76743 68000 = 15!
                                                             2092 27898 88000 = 16!
                                                            35568 74280 96000 = 17!
                                                          6 40237 37057 28000 = 18!
                                                        121 64510 04088 32000 = 19!
                                                       2432 90200 81766 40000 = 20!
                                                      51090 94217 17094 40000 = 21!
                                                   11 24000 72777 76076 80000 = 22!
                                                  258 52016 73888 49766 40000 = 23!
                                                 6204 48401 73323 94393 60000 = 24!
                                              1 55112 10043 33098 59840 00000 = 25!
                                             40 32914 61126 60563 55840 00000 = 26!
                                           1088 88694 50418 35216 07680 00000 = 27!
                                          30488 83446 11713 86050 15040 00000 = 28!
                                        8 84176 19937 39701 95454 36160 00000 = 29!
                                      265 25285 98121 91058 63630 84800 00000 = 30!
                                     8222 83865 41779 22817 72556 28800 00000 = 31!
                                  2 63130 83693 36935 30167 21801 21600 00000 = 32!
                                 86 83317 61881 18864 95518 19440 12800 00000 = 33!
                               2952 32799 03960 41408 47618 60964 35200 00000 = 34!
                            1 03331 47966 38614 49296 66651 33752 32000 00000 = 35!
                           37 19933 26789 90121 74679 99448 15083 52000 00000 = 36!
                         1376 37530 91226 34504 63159 79581 58090 24000 00000 = 37!
                        52302 26174 66601 11176 00072 24100 07429 12000 00000 = 38!
                     20 39788 20811 97443 35864 02817 39902 89735 68000 00000 = 39!
                    815 91528 32478 97734 34561 12695 96115 89427 20000 00000 = 40!
                  33452 52661 31638 07108 17006 20534 40751 66515 20000 00000 = 41!
               14 05006 11775 28798 98543 14260 62445 11569 93638 40000 00000 = 42!
              604 15263 06337 38356 37355 13206 85139 97507 26451 20000 00000 = 43!
            26582 71574 78844 87680 43625 81101 46158 90319 63852 80000 00000 = 44!
         11 96222 20865 48019 45619 63161 49565 77150 64383 73376 00000 00000 = 45!
        550 26221 59812 08894 98503 05428 80025 48929 61651 75296 00000 00000 = 46!
      25862 32415 11168 18064 29643 55153 61197 99691 97632 38912 00000 00000 = 47!
   12 41391 55925 36072 67086 22890 47373 37503 85214 86354 67776 00000 00000 = 48!
  608 28186 40342 67560 87225 21633 21295 37688 75528 31379 21024 00000 00000 = 49!
30414 09320 17133 78043 61260 81660 64768 84437 76415 68960 51200 00000 00000 = 50!