Initial commit

2020/day23/day23.c

@@ -0,0 +1,133 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define TEST_INPUT 389125467UL
+#define TEST_RESULT_10 92658374UL
+#define TEST_RESULT_100 67384529UL
+#define TEST_RESULT_PART2 149245887792UL
+#define INPUT 198753462UL
+
+void print_cups(unsigned long cups[static 1], unsigned long start) {
+  printf("(%lu) ", start);
+  unsigned long c = cups[start];
+  while (c != start) {
+    printf("%lu ", c);
+    if (c == 0) {
+      printf("\nreached zero, abort!\n");
+      return;
+    }
+    c = cups[c];
+  }
+  printf("\n");
+}
+
+unsigned long move(size_t size, unsigned long cups[size], unsigned long current) {
+  /* print_cups(cups, current); */
+  /* printf("current: %lu\n", current); */
+
+  unsigned long picked_up[3] = {0};
+  unsigned long c = current;
+  for (int i = 0; i < 3; ++i) {
+    picked_up[i] = cups[c];
+    c = cups[c];
+  }
+  /* printf("pick up: %lu, %lu, %lu\n", picked_up[0], picked_up[1],
+   * picked_up[2]); */
+
+  unsigned long dest = current - 1;
+  while ((dest == 0) || (dest == picked_up[0]) || (dest == picked_up[1]) ||
+         (dest == picked_up[2])) {
+    dest = (size + dest - 1) % size;
+  }
+  /* printf("destination: %lu\n", dest); */
+
+  cups[current] = cups[picked_up[2]];
+  cups[picked_up[2]] = cups[dest];
+  cups[dest] = picked_up[0];
+
+  return cups[current];
+}
+
+unsigned long *play(size_t size, unsigned long cups[size], unsigned long start,
+                    unsigned long steps) {
+  unsigned long current = start;
+  for (size_t i = 0; i < steps; ++i) {
+    /* printf("-- move %zu --\n", i+1); */
+    current = move(size, cups, current);
+  }
+
+  return cups;
+}
+
+unsigned long *init_cups(unsigned long n, size_t size) {
+  unsigned long *cups = calloc(size, sizeof(unsigned long));
+  unsigned long start = n / 100000000;
+
+  unsigned long q = n;
+  unsigned long r = start;
+  while (q != 0) {
+    cups[q % 10] = r;
+    r = q % 10;
+    q = q / 10;
+  }
+
+  if (size > 10) {
+    cups[n % 10] = 10;
+    for (size_t i = 10; i < size - 1; ++i) {
+      cups[i] = i + 1;
+    }
+    cups[size - 1] = start;
+  }
+
+  return cups;
+}
+
+unsigned long run_part(int part, unsigned long n, unsigned long steps) {
+  size_t size = 0;
+  if (part == 1) {
+    size = 10;
+  } else if (part == 2) {
+    size = 1000001;
+  }
+  unsigned long *cups = init_cups(n, size);
+  unsigned long start = n / 100000000;
+  play(size, cups, start, steps);
+
+  unsigned long res = 0;
+  if (part == 1) {
+    unsigned long c = cups[1];
+    while (c != 1) {
+      res = 10 * res + c;
+      c = cups[c];
+    }
+  } else if (part == 2) {
+    res = cups[1] * cups[cups[1]];
+  }
+
+  free(cups);
+  return res;
+}
+
+int main(int argc, char *argv[]) {
+  unsigned long res = 0;
+
+  res = run_part(1, TEST_INPUT, 10);
+  if (res != TEST_RESULT_10) {
+    printf("Test 1: %lu (expected = %lu)\n", res, TEST_RESULT_10);
+  }
+  res = run_part(1, TEST_INPUT, 100);
+  if (res != TEST_RESULT_100) {
+    printf("Test 2: %lu (expected = %lu)\n", res, TEST_RESULT_100);
+  }
+
+  printf("%lu\n", run_part(1, INPUT, 100));
+
+  res = run_part(2, TEST_INPUT, 10000000);
+  if (res != TEST_RESULT_PART2) {
+    printf("Test 3: %lu (expected = %lu)\n", res, TEST_RESULT_PART2);
+  }
+
+  printf("%lu\n", run_part(2, INPUT, 10000000));
+
+  return EXIT_SUCCESS;
+}

2020/day23/day23.rkt

@@ -0,0 +1,71 @@
+#lang racket
+
+(module+ test
+  (require rackunit))
+
+(define (labelling->cups num)
+  (define cups (make-vector 10 0))
+  (define start (quotient num 100000000))
+  (let loop ([prev start]
+             [n num])
+    (define-values (q r) (quotient/remainder n 10))
+    (vector-set! cups r prev)
+    (if (= q 0)
+        (values cups start)
+        (loop r q))))
+
+(define (cups->labelling cups)
+  (let loop ([idx (vector-ref cups 1)]
+             [num 0])
+    (if (= 1 idx)
+        num
+        (loop (vector-ref cups idx) (+ (* 10 num) idx)))))
+
+(define (move! cups current)
+  (define picked-up (let loop ([idxs (list (vector-ref cups current))]
+                               [i 0])
+                      (if (>= i 2)
+                          idxs
+                          (loop (cons (vector-ref cups (car idxs)) idxs) (add1 i)))))
+  (define destination (let loop ([d (sub1 current)])
+                        (if (or (= 0 d) (member d picked-up))
+                            (loop (modulo (sub1 d) (vector-length cups)))
+                            d)))
+  (vector-set! cups current (vector-ref cups (car picked-up)))
+  (vector-set! cups (car picked-up) (vector-ref cups destination))
+  (vector-set! cups destination (last picked-up))
+  (vector-ref cups current))
+
+(define (play! cups start steps)
+  (for/fold ([current start])
+            ([i (in-range steps)])
+    (move! cups current)))
+
+(define (part1 input steps)
+  (define-values (cups start) (labelling->cups input))
+  (play! cups start steps)
+  (cups->labelling cups))
+
+(module+ test
+  (check-equal? (part1 389125467 10) 92658374)
+  (check-equal? (part1 389125467 100) 67384529))
+
+(module+ main
+  (displayln (part1 198753462 100)))
+
+(define (part2 input)
+  (define-values (base-cups start) (labelling->cups input))
+  (define cups (make-vector 1000001 0))
+  (vector-copy! cups 0 base-cups)
+  (vector-set! cups (remainder input 10) 10)
+  (for ([i (in-range 10 1000000)])
+    (vector-set! cups i (add1 i)))
+  (vector-set! cups 1000000 start)
+  (play! cups start 10000000)
+  (* (vector-ref cups 1) (vector-ref cups (vector-ref cups 1))))
+
+(module+ test
+  (check-equal? (part2 389125467) 149245887792))
+
+(module+ main
+  (displayln (part2 198753462)))