ds-algo-study/DS-n-Algos/ALGO/factorial/factorial.js

Just experimenting with publishing a package

// Dynamic programming - factorial 

"use strict";
{

    const memory = [ 1, 1 ];

    Object.assign( self, { factorial_naive, factorial_recursive, factorial_dp } );

    test_factorial();

    function test_factorial () {
        const tests = [
            [ 10, 3628800 ],
            [ 4, 24 ],
            [ 12, 479001600 ],
            [ 1, 1 ],
            [ 2, 2 ],
            [ 0, 1 ]
        ];
        console.log(
            tests.map( ( [ a, r ] ) => factorial_naive( a ) == r ? `Naive passed ${ a } ${ r }` : `Naive failed ${ a } ${ r }` ).join( `\n` )
        );
        console.log(
            tests.map( ( [ a, r ] ) => factorial_recursive( a ) == r ? `Recursive passed ${ a } ${ r }` : `Recursive failed ${ a } ${ r }` ).join( `\n` )
        );
        console.log(
            tests.map( ( [ a, r ] ) => factorial_dp( a ) == r ? `DP passed ${ a } ${ r }` : `DP failed ${ a } ${ r }` ).join( `\n` )
        );
    }

    function factorial_naive ( n ) {
        if ( n <= 1 ) {
            return 1;
        } else {
            let result = n;
            while ( n > 1 ) {
                n -= 1;
                result *= n;
            }
            return result;
        }
    }

    function factorial_recursive ( n ) {
        if ( n <= 1 ) {
            return 1;
        }
        return n * factorial_recursive( n - 1 );
    }

    function factorial_dp ( n ) {
        if ( Number.isInteger( memory[ n ] ) ) {
            return memory[ n ];
        } else {
            if ( n <= 1 ) {
                return 1;
            }
            memory[ n ] = n * factorial_dp( n - 1 );
            return memory[ n ];
        }
    }

}