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hk7math
hk7math

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JavaScript CPU Emulator Problem

I've picked up CodeSignal again and aim to solve something every day (either challenges or casual problems). Recently, we got a medium challenge from hamlet_m1. It is to emulate a CPU assembly language. (Hope I didn't mix up technical terms).

This time, I'm proud to be one of the JS solvers together with other 8 geeks:

User Level Country Chars
Thomasz 70 USA 290
Giang_P_r 87 Vietnam 437
kov 93 Hungary 480
hk7math 44 Hong Kong 503
danielhong35 86 USA 512
murtaza_m2 43 Romania 921
omar-aguilar 62 Mexico 1367
linh_pv_9x 82 Vietnam 1490
jonathas_s1 24 Brazil 2198

The best solution by thomasz is an awe to me! Not only is it far shorter than all other solutions, but it is also still highly readable (to people like me who like hacky tricks)

Disclaimer: the full solution just for reference, please tell me to delete it if I violated any rule...

cpuEmulator = s => {

    z = 2 ** 32
    r = Array( 43 ).fill( 0 )
    R = x => +x.split`R`[ 1 ]

    for ( d = 0; l = s[ d++ ]; ) {

        [ c, a, b ] = l.split(/[\s,]/)
        o = y => r[ R( a ) ] = ( r[ R( a ) ] + y + z ) % z

        c == 'MOV' ?
            r[ R( b ) ] = R( a ) + 1 ? r[ R( a ) ] : +a  :            
        c == 'ADD' ?
            o( r[ R( b ) ] ) :
        c == 'DEC' ?
            o( -1 ) :
        c == 'INC' ?
            o( 1 ) :
        c == 'INV' ?
            o( ~r[ R( a ) ] * 2 + 1 ) :
        c == 'JMP' || c == 'JZ' && !r[ 0 ] ?
            d = +a - 1 : 0       
    }

    return r[ 42 ] + ''
}
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Here are some tricks I discovered in this snippet:

  1. Array(n).fill(x) to initialize an array of length n with prefilled values x (be careful about multi-dimension arrays though)
  2. +'numeric string' to cast a string as a number or NaN
  3. Regex /[xyz]/ to split string by separators x, y, z simultaneously
  4. c == 'case1' ? ... : c == 'case2' ? ... : ... to well format nested ternary operators as a switch-case
  5. number + '' to cast a number as a string

Feel free to drop a comment about your takeaways :D

Top comments (0)

In defense of the modern web

I expect I'll annoy everyone with this post: the anti-JavaScript crusaders, justly aghast at how much of the stuff we slather onto modern websites; the people arguing the web is a broken platform for interactive applications anyway and we should start over;

React users; the old guard with their artisanal JS and hand authored HTML; and Tom MacWright, someone I've admired from afar since I first became aware of his work on Mapbox many years ago. But I guess that's the price of having opinions.