Initial commit

2020/day15/day15.c

@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define SIZE 30000000
+
+size_t a[SIZE];
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <input list>\n", argv[0]);
+    return 0;
+  }
+
+  for (size_t i = 1; i < argc - 1; ++i) {
+    a[atoi(argv[i])] = i;
+  }
+
+  size_t n = atoi(argv[argc - 1]);
+  for (size_t i = argc - 1; i < SIZE; ++i) {
+    if (i == 2020) { // Part 1
+      printf("%zu\n", n);
+    }
+    size_t prev_n = n;
+    if (a[n] == 0) {
+      n = 0;
+    } else {
+      n = i - a[n];
+    }
+    a[prev_n] = i;
+  }
+  printf("%zu\n", n); // Part 2
+
+  return 0;
+}

2020/day15/day15.rkt

@@ -0,0 +1,39 @@
+#lang racket
+
+(module+ test
+  (require rackunit))
+
+(define (run-game input idx)
+  (define h (make-hash))
+  (for ([n (in-list (drop-right input 1))]
+        [i (in-naturals)])
+    (hash-set! h n (add1 i)))
+  (for/fold ([n (last input)])
+            ([i (in-range (length input) idx)])
+    (define res (- i (hash-ref h n i)))
+    (hash-set! h n i)
+    res))
+
+(module+ test
+  (check-equal? (run-game '(0 3 6) 2020) 436)
+  (check-equal? (run-game '(1 3 2) 2020) 1)
+  (check-equal? (run-game '(2 1 3) 2020) 10)
+  (check-equal? (run-game '(1 2 3) 2020) 27)
+  (check-equal? (run-game '(2 3 1) 2020) 78)
+  (check-equal? (run-game '(3 2 1) 2020) 438)
+  (check-equal? (run-game '(3 1 2) 2020) 1836))
+
+(module+ main
+  (displayln (run-game '(14 1 17 0 3 20) 2020)))
+
+(module+ test
+  (check-equal? (run-game '(0 3 6) 30000000) 175594)
+  (check-equal? (run-game '(1 3 2) 30000000) 2578)
+  (check-equal? (run-game '(2 1 3) 30000000) 3544142)
+  (check-equal? (run-game '(1 2 3) 30000000) 261214)
+  (check-equal? (run-game '(2 3 1) 30000000) 6895259)
+  (check-equal? (run-game '(3 2 1) 30000000) 18)
+  (check-equal? (run-game '(3 1 2) 30000000) 362))
+
+(module+ main
+  (displayln (run-game '(14 1 17 0 3 20) 30000000)))