Initial commit

2020/day10/day10.c

@@ -0,0 +1,63 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+
+int compare(const void* a, const void* b) {
+  unsigned int x = *(const unsigned int*)a;
+  unsigned int y = *(const unsigned int*)b;
+
+  if (x < y) return -1;
+  if (x > y) return 1;
+  return 0;
+}
+
+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;
+  }
+
+  unsigned int input[128] = {0};
+  unsigned int n = 1;
+  unsigned int d = 0;
+  unsigned int max = 0;
+  while (fscanf(fp, "%d\n", &d) == 1) {
+    input[n] = d;
+    n++;
+    max = d > max ? d : max;
+  }
+  max += 3;
+  input[n] = max;
+  n++;
+  fclose(fp);
+
+  qsort(input, n, sizeof(unsigned int), compare);
+
+  // Part 1
+  int ones = 0;
+  int threes = 0;
+  for (int i = 1; i < n; ++i) {
+    int diff = input[i] - input[i-1];
+    ones += (diff == 1);
+    threes += (diff == 3);
+  }
+  printf("%d\n", ones * threes);
+
+  // Part 2
+  unsigned long counts[1024] = {0};
+  counts[2] = 1;
+  for (int i = 1; i < n; ++i) {
+    unsigned int x = input[i];
+    counts[x+2] = counts[x-1] + counts[x] + counts[x+1];
+  }
+  printf("%lu\n", counts[max+2]);
+
+  return 0;
+}

2020/day10/day10.dyalog

@@ -0,0 +1,10 @@
+ ⎕IO←0 ⋄ ⎕PP←15
+ p←⍎¨⊃⎕NGET'input'1
+ p←0,p[⍋p],3+⌈/p
+ ×/⊢∘≢⌸2-/p  ⍝ Part 1
+ c←0,0,1,(⌈/p)⍴0  ⍝ paths counts
+ {c[⍵+2]←+/c[⍵+¯1 0 1]}¨1↓p
+ ⊃⌽c  ⍝ Part 2
+
+ a←(0∘<∧≤∘3)∘.-⍨p  ⍝ adjacency matrix
+ +/{⊃⊖({a+.×⍵}⍣⍵)a}¨⍳⍴p  ⍝ Part 2, the matrix way

2020/day10/day10.rkt

@@ -0,0 +1,49 @@
+#lang racket
+
+(module+ test
+  (require rackunit))
+
+(module+ main
+  (displayln "Day 10"))
+
+(define (read-input filename)
+  (define input (map string->number (file->lines filename)))
+  (sort (cons 0 (cons (target input) input)) <))
+
+(define (target lst)
+  (+ 3 (apply max lst)))
+
+(define (part1 filename)
+  (define jolts (read-input filename))
+  (define counts (make-hash))
+  (for ([x (in-list (drop jolts 1))]
+        [y (in-list jolts)])
+    (hash-update! counts (- x y) add1 0))
+  (* (hash-ref counts 1 0) (hash-ref counts 3 0)))
+
+(module+ test
+  (check-equal? (part1 "test1") (* 7 5))
+  (check-equal? (part1 "test2") (* 22 10)))
+
+(module+ main
+  (displayln (part1 "input")))
+
+(define (count-paths jolts)
+  (define counts (make-hash))
+  (hash-set! counts 0 1)
+  (for ([x (in-list (cdr jolts))])
+    (hash-set! counts x (+ (hash-ref counts (- x 1) 0)
+                           (hash-ref counts (- x 2) 0)
+                           (hash-ref counts (- x 3) 0))))
+  (hash-ref counts (last jolts)))
+
+(define (part2 filename)
+  (define jolts (read-input filename))
+  (count-paths jolts))
+
+(module+ test
+  (check-equal? (part2 "test1") 8)
+  (check-equal? (part2 "test2") 19208))
+
+(module+ main
+  (displayln (part2 "input")))

2020/day10/input

@@ -0,0 +1,95 @@
+86
+149
+4
+75
+87
+132
+12
+115
+62
+61
+153
+78
+138
+43
+88
+108
+59
+152
+109
+63
+42
+60
+7
+104
+49
+156
+35
+2
+52
+72
+125
+94
+46
+136
+26
+16
+76
+117
+116
+150
+20
+13
+141
+131
+127
+67
+3
+40
+54
+82
+36
+100
+41
+56
+146
+157
+89
+23
+8
+55
+111
+135
+144
+77
+124
+18
+53
+92
+126
+101
+69
+27
+145
+11
+151
+31
+19
+34
+17
+130
+118
+28
+107
+137
+68
+93
+85
+66
+97
+110
+37
+114
+79
+121
+1

2020/day10/test1

@@ -0,0 +1,11 @@
+16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4

2020/day10/test2

@@ -0,0 +1,31 @@
+28
+33
+18
+42
+31
+14
+46
+20
+48
+47
+24
+23
+49
+45
+19
+38
+39
+11
+1
+32
+25
+35
+8
+17
+7
+9
+4
+2
+34
+10
+3