d2s2.jl

using OffsetArrays
using Test

const input = parse.(Int, split(read("2_input", String), ','))

const instructions = Dict(
    1 => +,
    2 => *,
)

function init!(intcode, noun, verb)
    intcode[1] = noun
    intcode[2] = verb
    return intcode
end

function main(input, noun, verb)
    intcode = OffsetVector(copy(input), 0:length(input) - 1)

    # 1202 program alarm
    # init!(intcode, 12, 2)
    init!(intcode, noun, verb)

    i = 0
    while intcode[i] != 99
        intcode[intcode[i + 3]] = instructions[intcode[i]](intcode[intcode[i + 1]], intcode[intcode[i + 2]])
        i += 4
    end
    return intcode[0]
end

function reverse(input, output)
    for i in 0:99, j in 0:99
        main(input, i, j) == output && return 100 * i + j
    end
end

function tests()
    @test main(input, 12, 2) == 5866714
end

I like that you called it reverse :)