day 9

src/day09/README.md

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+# 🎄 Advent of Code 2024 - day 9 🎄
+
+## Info
+
+Task description: [link](https://adventofcode.com/2024/day/9)
+
+## Notes
+
+...

src/day09/index.ts

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+import run from "aocrunner"
+
+const parseInput = (rawInput: string) => rawInput.split('').map(Number)
+
+const part1 = (rawInput: string) => {
+  const input = parseInput(rawInput)
+  let mem: number[] = []
+  let space = 0
+  for (let i = 0; i < input.length; i+= 2) {
+    const [f,s] = input.slice(i,i+2)
+    mem.push(...(new Array(f).fill(i/2)))
+    mem.push(...(new Array(s).fill(-1)))
+    space += s
+  }
+  for (let from = mem.length - 1; from >= 0; from--) {
+    if (mem[from] < 0) continue
+    const to = mem.findIndex(x => x < 0)
+    if (to === -1 || to > from) break
+    mem[to] = mem[from]
+    mem[from] = -1
+  }
+  return mem.reduce((total, b, i) => {
+    if (b < 0) return total
+    return total + b * i
+  }, 0)
+}
+
+const part2 = (rawInput: string) => {
+  const input = parseInput(rawInput)
+  let files: number[][] = [] // [index, length]
+  let spaces: number[][] = []
+  for (let i = 0, cursor = 0; i < input.length; i+= 2) {
+    const [f,s] = input.slice(i,i+2)
+    files.push([cursor, f])
+    cursor += f
+    if (s === undefined) continue
+    spaces.push([cursor, s])
+    cursor += s
+  }
+  for (let i = files.length - 1; i >= 0; i--) {
+    const file = files[i]
+    const space = spaces.find(space => space[1] >= file[1])
+    spaces.pop() // remove the space to the left of this file, which can no longer be used
+    if (space === undefined) {
+      continue
+    }
+    space[1] -= file[1]
+    const newSpaceIndex = space[0] + file[1]
+    file[0] = space[0]
+    space[0] = newSpaceIndex
+  }
+  return files.reduce((total, [index,length], id) => {
+    return total + id * length * (2*index + length - 1) / 2
+  }, 0)
+}
+
+run({
+  part1: {
+    tests: [
+      {
+        input: `2333133121414131402`,
+        expected: 1928,
+      },
+    ],
+    solution: part1,
+  },
+  part2: {
+    tests: [
+      {
+        input: `2333133121414131402`,
+        expected: 2858,
+      },
+    ],
+    solution: part2,
+  },
+  trimTestInputs: true,
+  onlyTests: false,
+})