2020 day 20 part 1

2020/20/part1.js

@@ -0,0 +1,43 @@
+const fs = require('fs');
+const input = fs.readFileSync('./input.txt', 'utf-8');
+
+const inputTiles = input.split('\n\n');
+
+// it is implied that the image is a square, which makes it far simpler.
+const sideLength = Math.sqrt(inputTiles.length);
+const tileSize = 9
+let allBorders = new Map();
+console.log(sideLength);
+let tiles = [];
+inputTiles.forEach(inputTile => {
+  tileLines = inputTile.split('\n');
+  let tileID = tileLines[0].slice(5, 9);
+  let tileData = tileLines.slice(1)
+  let borders = [
+    tileData[0], 
+    tileData[tileSize],
+    tileData.reduce((a,b)=>a+b[0], ''),
+    tileData.reduce((a,b)=>a+b[tileSize], '')
+  ];
+  borders.forEach(border=>{
+    if (!allBorders.has(border)) {
+      allBorders.set(border, 1)
+    } else {
+      allBorders.set(border, allBorders.get(border) + 1)
+    }
+  })
+  tiles.push({tileID, borders})
+})
+
+function reverseString(str) {
+  return (str === '') ? '' : reverseString(str.substr(1)) + str.charAt(0);
+}
+
+let runningTotal = 1;
+tiles.forEach(tile => {
+  if (tile.borders.reduce((a, border) => a + allBorders.get(border) + (allBorders.get(reverseString(border))||0), -4) == 2) {
+    console.log(tile.tileID)
+    runningTotal *= tile.tileID
+  }
+})
+console.log(runningTotal)

2020/20/test.txt

@@ -0,0 +1,107 @@
+Tile 2311:
+..##.#..#.
+##..#.....
+#...##..#.
+####.#...#
+##.##.###.
+##...#.###
+.#.#.#..##
+..#....#..
+###...#.#.
+..###..###
+
+Tile 1951:
+#.##...##.
+#.####...#
+.....#..##
+#...######
+.##.#....#
+.###.#####
+###.##.##.
+.###....#.
+..#.#..#.#
+#...##.#..
+
+Tile 1171:
+####...##.
+#..##.#..#
+##.#..#.#.
+.###.####.
+..###.####
+.##....##.
+.#...####.
+#.##.####.
+####..#...
+.....##...
+
+Tile 1427:
+###.##.#..
+.#..#.##..
+.#.##.#..#
+#.#.#.##.#
+....#...##
+...##..##.
+...#.#####
+.#.####.#.
+..#..###.#
+..##.#..#.
+
+Tile 1489:
+##.#.#....
+..##...#..
+.##..##...
+..#...#...
+#####...#.
+#..#.#.#.#
+...#.#.#..
+##.#...##.
+..##.##.##
+###.##.#..
+
+Tile 2473:
+#....####.
+#..#.##...
+#.##..#...
+######.#.#
+.#...#.#.#
+.#########
+.###.#..#.
+########.#
+##...##.#.
+..###.#.#.
+
+Tile 2971:
+..#.#....#
+#...###...
+#.#.###...
+##.##..#..
+.#####..##
+.#..####.#
+#..#.#..#.
+..####.###
+..#.#.###.
+...#.#.#.#
+
+Tile 2729:
+...#.#.#.#
+####.#....
+..#.#.....
+....#..#.#
+.##..##.#.
+.#.####...
+####.#.#..
+##.####...
+##..#.##..
+#.##...##.
+
+Tile 3079:
+#.#.#####.
+.#..######
+..#.......
+######....
+####.#..#.
+.#...#.##.
+#.#####.##
+..#.###...
+..#.......
+..#.###...

README.md

@@ -60,3 +60,4 @@ if (advent) {
 17. [:star: :star:](https://adventofcode.com/2020/day/17 "see puzzle")
 18. [:star: :star:](https://adventofcode.com/2020/day/18 "see puzzle")
 19. [:star:](https://adventofcode.com/2020/day/19 "see puzzle")
+20. [:star:](https://adventofcode.com/2020/day/20 "see puzzle")