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Colin Fay
Colin Fay

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Advent of Code 2019-02 with R & JavaScript

#rstats #adventofcode #javascript

Solving Advent of Code 2019-02 with R and JavaScript.

[Disclaimer] Obviously, this post contains a big spoiler about Advent
of Code, as it gives solutions for solving day 2.

[Disclaimer bis] I’m no JavaScript expert so this might not be the
perfect solution. And TBH, that’s also the case for the R solution.

About the JavaScript code

The JavaScript code has been written in the same RMarkdown as the R
code. It runs thanks to the {bubble} package:
https://github.com/ColinFay/bubble

Instructions

Find the instructions at: https://adventofcode.com/2019/day/2

R solution

When in doubt, use brute force.

Ken Thompson

Part one 

extract <- function(vec, idx) vec[as.character(idx)] day_2 <- function(vec, one = 12, two = 2){ vec[2] <- one vec[3] <- two names(vec) <- 0:(length(vec) - 1) start <- 0 repeat { req <- extract(vec, start) if (req == 99) break if (req == 1) fun <- `+` if (req == 2) fun <- `*` vec[as.character( extract(vec, start + 3) )] <- fun( extract(vec, extract(vec, start + 1)), extract(vec, extract(vec, start + 2)) ) start <- start + 4 } vec[1] } ipt <- scan( "input2.txt", what = numeric(), sep = ",") day_2(ipt)
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## 0 ## 3409710
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Part two 

x <- purrr::cross2(0:99, 0:99) i <- 1 repeat{ res <- day_2(ipt, x[[i]][[1]], x[[i]][[2]]) if (res == 19690720) break i <- i + 1 } # Answer 100 * x[[i]][[1]] + x[[i]][[2]]
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## [1] 7912
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JS solution

Part one & Two

// Reading the file

var res = fs.readFileSync("input2.txt", 'utf8').split(",").filter(x => x.length != 0); var res = res.map(x => parseInt(x));
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function day_2(vec, one = 12, two = 2){ var loc = vec.slice(); loc[1] = one; loc[2] = two; start = 0; do { var req = loc[start]; if (req === 99){ break; } pos1 = loc[start + 1]; pos2 = loc[start + 2]; pos3 = loc[start + 3]; if (req === 1){ loc[pos3] = loc[pos1] + loc[pos2]; } else if (req === 2){ loc[pos3] = loc[pos1] * loc[pos2]; } start = start + 4; } while (start < vec.length) return loc[0] }
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day_2(res)
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## 3409710
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function make_array(l){ return Array.from({length: l}, (el, index) => index); } var x = make_array(100); var y = make_array(100); var cross = []; for (var i = 0; i < x.length; i++){ for (var j = 0; j < y.length; j++){ cross.push( [x[i], y[j]] ) } } i = 0 do { ans = day_2(res, cross[i][0], cross[i][1]); if (ans == 19690720) break i++ } while (i < cross.length)
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100 * cross[i][0] + cross[i][1]
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## 7912
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Day 2 takeaway

  • Array.from({length: n}, (el, index) => index); is more or less the
    equivalent of R 1:n

  • When doing [] = in JS, we’re modifying the original objet. Compare

# R x <- 1:3 x
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## [1] 1 2 3
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plop <- function(y){ y[1] <- 2 } plop(x) x
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## [1] 1 2 3
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to

// JS var x = [1, 2, 3]; function yeay(ipt){ ipt[1] = 12 } yeay(x)
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x
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## [ 1, 12, 3 ]
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  • JavaScript copies by reference. Compare:
# R  x <- 1:3 y <- x x[1] <- 999 x
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## [1] 999 2 3
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y
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## [1] 1 2 3
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And

var x = make_array(3); var y = x x[1] = 999
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x y
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## [ 0, 999, 2 ] ## [ 0, 999, 2 ]
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  • This can be prevented with obj.slice() 
var x = make_array(10); var y = x.slice(); x[1] = 999
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x y
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## [ 0, 999, 2, 3, 4, 5, 6, 7, 8, 9 ] ## [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
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