Solve day 15 ⚠️

Author: memoriesadrift

src/day14.ts

@@ -1,7 +1,7 @@
 import {_} from './util/lodash.ts'
 import {getInput, printSolutions} from './util/io.ts'
+import type {Coord} from './util/types.ts'
 
-type Coord = {x: number, y: number}
 type Tile = "sand" | "rock"
 
 const buildMap = (coords: Coord[]): Map<string, Tile> => {

src/day15.ts

@@ -0,0 +1,106 @@
+// First day where I had no clue what to do...
+// Solution I based mine on: https://www.reddit.com/r/adventofcode/comments/zmcn64/comment/j0axxpo
+
+import {_} from './util/lodash.ts'
+import {getInput, printSolutions} from './util/io.ts'
+import type {Coord} from './util/types.ts'
+
+type DataPoint = {
+  sensor: Coord
+  beacon: Coord
+}
+
+const parseInput = (input: string[]) => {
+  return input.map((line): DataPoint => {
+    const firstSlice = line
+      .slice(
+        line.indexOf('x='),
+        line.indexOf(':'))
+      .split(',')
+      .map((it) => Number.parseInt(it.trim().slice(2)))
+
+    const secondSlice = line
+      .slice(line.indexOf('is at') + 'is at'.length)
+      .split(',')
+      .map((it) => Number.parseInt(it.trim().slice(2)))
+
+    return {
+      sensor: {
+        x: firstSlice[0],
+        y: firstSlice[1],
+      },
+      beacon: {
+        x: secondSlice[0],
+        y: secondSlice[1],
+      }
+    }
+  })
+}
+
+const solve1 = (input: string[]) => {
+  const row = 2000000
+
+  const resultSet = new Set()
+
+  // .map() has failed me... or have I failed .map()..?
+  parseInput(input).forEach(({sensor, beacon}) => {
+    const dist = Math.abs(sensor.x - beacon.x) + Math.abs(sensor.y - beacon.y)
+    const restDist = dist - Math.abs(row - sensor.y)
+    
+    if (restDist < 0) {
+      return
+    }
+
+    if (!(sensor.x === beacon.x && row === beacon.y)) {
+      resultSet.add(sensor.x)
+    }
+
+    for(let i = 1; i < restDist + 1; i += 1) {
+      if (!(sensor.x - i === beacon.x && row === beacon.y)) {
+        resultSet.add(sensor.x - i)
+      }
+
+      if (!(sensor.x + i === beacon.x && row === beacon.y)) {
+        resultSet.add(sensor.x + i) 
+      }
+    }
+  })
+
+  return resultSet.size
+}
+
+const solve2 = (input: string[]) => {
+  for (let row = 0; row <= 4000000; row += 1) {
+    const ranges: {start: number, end: number}[] = []
+    parseInput(input).forEach(({sensor, beacon}) => {
+      const dist = Math.abs(sensor.x - beacon.x) + Math.abs(sensor.y - beacon.y)
+      const restDist = dist - Math.abs(row - sensor.y)
+
+      if (restDist < 0) return
+      ranges.push({start: sensor.x - restDist, end: sensor.x + restDist})
+    })
+
+    ranges.sort((a, b) => a.start - b.start)
+    const merged = []
+    for (let i = 0; i < ranges.length - 1; i += 1) {
+      const curr = ranges[i]
+      const next = ranges[i+1]
+
+      if ((next.start <= curr.end && curr.end <= next.end) || next.start === curr.end + 1) {
+        ranges[i + 1] = {start: curr.start, end: next.end}
+      } else if (curr.start <= next.start && curr.end >= next.end) {
+        ranges[i + 1] = curr
+      } else {
+        merged.push(curr)
+      }
+    }
+    merged.push(ranges[ranges.length - 1])
+    if (merged.length > 1) {
+      return (merged[0].end + 1) * 4000000 + row
+    }
+  }
+}
+
+const input = await getInput(15, false)
+printSolutions(solve1, solve2, input)
+

src/util/types.ts

@@ -8,3 +8,8 @@ export type Pair<T, U> = {
   second: U
 }
 
+export type  Coord = {
+  x: number
+  y: number
+}
+