ds-algo-study/DS-n-Algos/ALGO/Dynamic-Programming/primes.js

Just experimenting with publishing a package

// Dynamic programming - primes

"use strict";
{
    const memory = [ 2, 3, 5, 7 ];

    test_primes();

    function test_primes () {
        console.log( [
            nthPrime( 5 ),
            nthPrime( 15 ),
            nthPrime( 50 ),
            nthPrime( 500 )
        ] );
        console.log( memory );
    }

    // Idea is we use existing primes as dividers for testing the next prime

    function nthPrime ( n ) {
        if ( n < 0 ) {
            throw new TypeError( "N > 0" );
        }
        if ( n < 4 ) {
            return memory[ n ];
        }
        const lastPrime = memory.pop();
        memory.push( lastPrime );
        let nextCandidate = lastPrime + 2;
        testCandidates: while ( memory.length < n ) {
            const maxDivider = Math.floor( Math.sqrt( nextCandidate ) );
            let i = 0;
            testDividers: while ( memory[ i ] <= maxDivider ) {
                if ( nextCandidate % memory[ i ] == 0 ) {
                    nextCandidate += 2;
                    continue testCandidates;
                }
                i += 1;
            }
            const nextPrime = nextCandidate;
            memory.push( nextPrime );
            if ( memory.length < n ) {
                nextCandidate = nextPrime + 2;
                continue testCandidates;
            } else {
                break;
            }
        }
        return memory[ n - 1 ];
    }
}