initial commit

.gitignore

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+*.in
+.metals/

README.md

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+# Advent of Code 2021
+
+| Day | Chicken Scheme | Scala  | Python | Nim |   |
+|-----|----------------|--------|--------|-----|---|
+| 1   |                |        |        |     |   |
+| 2   |                |        |        |     |   |
+| 3   | part 1         | part 1 | ✅     |     |   |
+| 4   |                |        | ✅     |     |   |
+| 5   |                |        | ✅     |     |   |
+| 6   |                |        |        | ✅  |   |

day03.py

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+#!/usr/bin/env python3
+import fileinput
+from copy import deepcopy
+
+numbers = [[int(i) for i in line.strip()] for line in fileinput.input()]
+bit_count = len(numbers[0])
+
+occurrences = [0] * bit_count
+for number in numbers:
+    for i, bit in enumerate(number):
+        occurrences[i] += bit
+
+gamma, epsilon = 0, 0
+for i, freq in enumerate(occurrences):
+    shifted = 1 << (len(occurrences) - 1) >> i
+    if freq > len(numbers) // 2:
+        gamma |= shifted
+    else:
+        epsilon |= shifted
+
+print("part 1:", gamma * epsilon)
+
+most_common = deepcopy(numbers)
+least_common = deepcopy(numbers)
+
+for i in range(bit_count):
+    ones = sum(number[i] for number in most_common)
+    lc = int(ones * 2 >= len(most_common))
+    most_common = [number for number in most_common if number[i] == lc]
+    if len(most_common) == 1:
+        break
+
+for i in range(bit_count):
+    zeros = sum(not number[i] for number in least_common)
+    lc = int(zeros * 2 > len(least_common))
+    least_common = [number for number in least_common if number[i] == lc]
+    if len(least_common) == 1:
+        break
+
+mc = int("".join(str(x) for x in most_common[0]), 2)
+lc = int("".join(str(x) for x in least_common[0]), 2)
+print("part 2:", mc * lc)

day03.scala

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+object day03 {
+  def main(args: Array[String]): Unit = {
+    val numbers = io.Source.stdin
+      .getLines()
+      .map(ln => ln.chars.map(_ - '0').toArray)
+      .toArray
+
+    var occurences = Array.fill(numbers(0).length)(0)
+    for (number <- numbers) {
+      for ((bit, i) <- number.zipWithIndex)
+        occurences(i) += bit
+    }
+
+    var gamma = 0
+    var epsilon = 0
+    for ((freq, i) <- occurences.zipWithIndex) {
+      val shifted = 1 << occurences.length - 1 >> i
+      if (freq > (numbers.length / 2))
+        gamma |= shifted
+      else
+        epsilon |= shifted
+    }
+
+    val part1 = gamma * epsilon
+    println(s"part1: $part1")
+  }
+}

day03.scm

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+(import (chicken string))
+(import (chicken format))
+(import (chicken io))
+(import srfi-14)
+(import srfi-60)
+
+(define (add-lines l r)
+  (map (lambda (l r) (+ l (- (char->integer r) 48))) l r))
+
+(define lines (map string->list (read-lines)))
+(define counts (foldl add-lines (map (lambda (_) 0) (car lines)) lines))
+
+(define hl (/ (length lines) 2))
+(define gamma (list->integer (map (lambda (x) (> x hl)) counts)))
+(define epsilon (list->integer (map (lambda (x) (< x hl)) counts)))
+
+(format #t "part 1: ~A~%" (* gamma epsilon))

day04.py

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+import fileinput
+from typing import List, Tuple, Set
+
+numbers = [int(x) for x in input().split(",")]
+input()
+
+Board = List[List[int]]
+
+boards: List[Board] = []
+board: Board = []
+
+while True:
+    try:
+        line = input().strip()
+    except EOFError:
+        break
+
+    if line:
+        board.append([int(x) for x in line.split()])
+    else:
+        boards.append(board)
+        board = []
+
+if board:
+    boards.append(board)
+
+
+def find_bingo(drawn: Set[int], wins: Set[int]) -> Tuple[int, int]:
+    for n in numbers:
+        drawn.add(n)
+
+        for b, board in enumerate(boards):
+            for row in board:
+                for col in row:
+                    if col not in drawn:
+                        break
+                else:
+                    if b not in wins:
+                        wins.add(b)
+                        return b, n
+
+            for x in range(len(board[0])):
+                for y in range(len(board)):
+                    if board[y][x] not in drawn:
+                        break
+                else:
+                    if b not in wins:
+                        wins.add(b)
+                        return b, n
+
+    raise RuntimeError("no bingo found")
+
+
+def print_board(board, drawn=frozenset()):
+    for r in board:
+        for c in r:
+            if c in drawn:
+                print("\033[91m", end="")
+            print(str(c).rjust(4), end="\033[0m")
+        print()
+    print()
+
+
+print(", ".join(str(n) for n in numbers))
+print()
+for b in boards:
+    print_board(b)
+
+print("===")
+
+drawn = set()
+wins = set()
+
+b, last_drawn = find_bingo(drawn, wins)
+undrawn = sum(number for row in boards[b] for number in row if number not in drawn)
+part1 = last_drawn * undrawn
+
+while len(wins) < len(boards):
+    b, last_drawn = find_bingo(drawn, wins)
+    print_board(boards[b], drawn)
+
+undrawn = sum(number for row in boards[b] for number in row if number not in drawn)
+part2 = last_drawn * undrawn
+
+print("part1:", part1)
+print("part2:", part2)

day05.py

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+#!/usr/bin/env python3
+import fileinput
+
+N = 1000
+
+
+def main():
+    diag = [[0] * N for _ in range(N)]
+
+    vents = [
+        [
+            tuple(int(coord) for coord in coords.split(","))
+            for coords in str(line).split(" -> ")
+        ]
+        for line in fileinput.input()
+    ]
+
+    for (x1, y1), (x2, y2) in vents:
+        xsign = -1 if x2 < x1 else 1
+        ysign = -1 if y2 < y1 else 1
+
+        if x1 == x2:
+            # vertical line
+            for y in range(y1, y2 + ysign, ysign):
+                diag[y][x1] += 1
+        elif y1 == y2:
+            # horizontal line
+            for x in range(x1, x2 + xsign, xsign):
+                diag[y1][x] += 1
+
+    part1 = sum(point >= 2 for row in diag for point in row)
+    print("part 1:", part1)
+
+    for (x1, y1), (x2, y2) in vents:
+        xsign = -1 if x2 < x1 else 1
+        ysign = -1 if y2 < y1 else 1
+
+        if x1 != x2 and y1 != y2:
+            # diagonal line
+            y = y1
+            for x in range(x1, x2 + xsign, xsign):
+                diag[y][x] += 1
+                y += ysign
+
+    part2 = sum(point >= 2 for row in diag for point in row)
+    print("part 2:", part2)
+
+
+if __name__ == "__main__":
+    main()

day06.nim

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+from std/strutils import split, parseInt
+from std/sequtils import map, foldl
+
+let numbers = readLine(stdin).split(',').map(parseInt)
+var buckets: array[9, int]
+
+for number in numbers:
+  buckets[number] += 1
+
+for i in 0..<256:
+  buckets[(i + 7) mod 9] += buckets[i mod 9]
+
+  if i == 79:
+    echo("part 1: ", buckets.foldl(a + b))
+
+echo("part 2: ", buckets.foldl(a + b))