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commit 6fbdad0ba52401ad8b286099882b60ab07701dec
parent 4d9011d5fcbe2e275a11b2688b261426b3bf50df
Author: Luís Ferreira <[email protected]>
Date:   Fri, 17 Dec 2021 23:09:19 +0000

posts: Add 'Solution in D for Advent of Code 2021, Day 4'

Signed-off-by: Luís Ferreira <[email protected]>

Diffstat:
Acontent/posts/zet-5-aoc-2021-04.md | 87+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 87 insertions(+), 0 deletions(-)

diff --git a/content/posts/zet-5-aoc-2021-04.md b/content/posts/zet-5-aoc-2021-04.md @@ -0,0 +1,87 @@ +--- +title: 'Zettelkasten #5: Solution in D for Advent of Code 2021, Day 4' +date: '2021-12-17T22:04:00+01:00' +tags: ['zettelkasten', 'zet', 'dlang', 'aoc', 'aoc2021', 'adventofcode'] +description: "This post describes my solution in the D programming language for +the 4th puzzle of the Advent of Code 2021." +--- + +## The challenge + +> You're already almost 1.5km (almost a mile) below the surface of the ocean, +> already so deep that you can't see any sunlight. What you can see, however, +> is a giant squid that has attached itself to the outside of your submarine. +> +> Maybe it wants to play bingo? +> +> Bingo is played on a set of boards each consisting of a 5x5 grid of numbers. +> Numbers are chosen at random, and the chosen number is marked on all boards +> on which it appears. (Numbers may not appear on all boards.) If all numbers +> in any row or any column of a board are marked, that board wins. (Diagonals +> don't count.) +> +> [...] +> +> To guarantee victory against the giant squid, figure out which board will win +> first. What will your final score be if you choose that board? + +You can read the challenge more in depth, +[here](https://adventofcode.com/2021/day/4). + +## Part 1 + +### Full solution + +```d +auto input = [stdin.byLineCopy().array].map!(a => [ // input + a.front.splitter(",").map!(to!long).array, // parse numbers + a[1..$].map!`a.splitter(" ").filter!"!a.empty".map!(to!long)` // parse cards + .joiner.array]).front; +immutable ncards = input[1].length / 25; // calc number of cards +foreach(pos, i; input[0]) foreach(c; 0..ncards) { // for each number & card + foreach(n; 0..25) if(input[1][c*25 + n] == i) input[1][c*25 + n] = -1; // set matching numbers + auto e = evenChunks(input[1][c*25..c*25+25],5).array; // construct card RoR + foreach(el; zip(e, e.dup.transposed)) if(findSkip(el[0], repeat(-1L,5)) // find row + || findSkip(el[1], repeat(-1L,5))) { // find column + writeln(input[1][c*25..c*25+25].filter!"a != -1".sum * i); // calculate result + return; // hang + } +} +``` + +## Part 2 + +> On the other hand, it might be wise to try a different strategy: let the +> giant squid win. +> +> You aren't sure how many bingo boards a giant squid could play at once, so +> rather than waste time counting its arms, the safe thing to do is to figure +> out which board will win last and choose that one. That way, no matter which +> boards it picks, it will win for sure. +> +> [...] +> +> Figure out which board will win last. Once it wins, what would its final +> score be? + +### Full solution + +```d +auto input = [stdin.byLineCopy().array].map!(a => [ // input + a.front.splitter(",").map!(to!long).array, // parse numbers + a[1..$].map!`a.splitter(" ").filter!"!a.empty".map!(to!long)` // parse cards + .joiner.array]).front; +immutable ncards = input[1].length / 25; // calc number of cards +bool[] winners = new bool[ncards]; +foreach(pos, i; input[0]) foreach(c; 0..ncards) { // for each number & card + foreach(n; 0..25) if(input[1][c*25 + n] == i) input[1][c*25 + n] = -1; // set matching numbers + auto e = evenChunks(input[1][c*25..c*25+25],5).array; // construct card RoR + foreach(el; zip(e, e.dup.transposed)) if(findSkip(el[0], repeat(-1L,5)) // find row + || findSkip(el[1], repeat(-1L,5))) { // find column + winners[c] = true; if(winners.all) { // fill winners list & check + writeln(input[1][c*25..c*25+25].filter!"a != -1".sum * i); // calculate result + return; // hang + } + } +} +```