Initial commit

2020/day03/day03.c

@@ -0,0 +1,79 @@
+#include <stdbool.h>
+#include <stdio.h>
+
+int count_lines(FILE *fp) {
+  int count = 0;
+
+  for (char c = getc(fp); c != EOF; c = getc(fp)) {
+    if (c == '\n') {
+      count++;
+    }
+  }
+  return count;
+}
+
+int line_length(FILE *fp) {
+  int count = 0;
+
+  for (char c = getc(fp); c != '\n'; c = getc(fp)) {
+    count++;
+  }
+
+  return count;
+}
+
+int count_trees(int n, int m, int grid[n][m], int down_offset, int right_offset) {
+  int count = 0;
+
+  for (int i = 0; i < n / down_offset; ++i) {
+    count += grid[i * down_offset][i * right_offset % m];
+  }
+
+  return count;
+}
+
+int main(int argc, char *argv[])
+{
+  if (argc < 2) {
+    printf("Usage: %s <input file>\n", argv[0]);
+    return 0;
+  }
+
+  FILE *fp = fopen(argv[1], "r");
+  if (fp == NULL) {
+    printf("Could not open file %s\n", argv[1]);
+    return 1;
+  }
+
+  int n = count_lines(fp);
+  rewind(fp);
+  int m = line_length(fp);
+  rewind(fp);
+
+  printf("Grid size: %d×%d\n", n, m);
+
+  int grid[n][m];
+  char c;
+  for (int i = 0; i < n; ++i) {
+    for (int j = 0; j < m; ++j) {
+      c = getc(fp);
+      if (c == '\n' || c == EOF) {
+	c = getc(fp);
+      }
+      grid[i][j] = (c == '#');
+    }
+  }
+  fclose(fp);
+
+  printf("%d\n", count_trees(n, m, grid, 1, 3));
+
+  int total = 1;
+  int down_offsets[] = {1, 1, 1, 1, 2};
+  int right_offsets[] = {1, 3, 5, 7, 1};
+  for (int i = 0; i < 5; ++i) {
+    total *= count_trees(n, m, grid, down_offsets[i], right_offsets[i]);
+  }
+  printf("%d\n", total);
+
+  return 0;
+}

2020/day03/day03.dyalog

@@ -0,0 +1,5 @@
+ ⎕io←0
+ p←'#'=↑⊃⎕NGET'input'1
+ f←{+/p[↓⍉↑(⍴p)|⍵×2⍴⊂⍳⌈(⊃⍴p)÷⊃⍵]}
+ f 1 3  ⍝ Part 1
+ ×/f¨(1 1)(1 3)(1 5)(1 7)(2 1)  ⍝ Part 2

2020/day03/day03.rkt

@@ -0,0 +1,52 @@
+#lang racket
+
+(module+ test
+  (require rackunit))
+
+(module+ main
+  (displayln "Day 3"))
+
+(define (parse-line str)
+  (list->vector
+   (map (λ (c) (if (equal? c #\#) 1 0)) (string->list str))))
+
+(define (read-input filename)
+  (with-input-from-file filename
+    (lambda ()
+      (for/vector ([line (in-lines)])
+        (parse-line line)))))
+
+(define (traj grid down right)
+  (define height (vector-length grid))
+  (define width (vector-length (vector-ref grid 0)))
+  (for/list ([line (in-vector grid 0 #f down)]
+             [j (in-range 0 (* width height right) right)])
+    (vector-ref line (remainder j width))))
+
+(define (part1 filename)
+  (define grid (read-input filename))
+  (apply + (traj grid 1 3)))
+
+(module+ test
+  (check-equal? (part1 "test") 7))
+
+(module+ main
+  (displayln (part1 "input")))
+
+(define slopes
+  '((1 1)
+    (1 3)
+    (1 5)
+    (1 7)
+    (2 1)))
+
+(define (part2 filename)
+  (define grid (read-input filename))
+  (for/product ([slope slopes])
+    (apply + (traj grid (car slope) (cadr slope)))))
+
+(module+ test
+  (check-equal? (part2 "test") 336))
+
+(module+ main
+  (displayln (part2 "input")))

2020/day03/input

@@ -0,0 +1,323 @@
+...........#..............##...
+...#....................#......
+.....####...........#.#..#.#...
+....##.#.......................
+.......#.##......#.###.........
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2020/day03/test

@@ -0,0 +1,11 @@
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
+.#.#.#....#
+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#