Aaaaaaaaaaaaaaagh

c/2024/11/plutonian_pebbles.c

@@ -0,0 +1,141 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <limits.h>
+
+#include "../../lib/aoc.h"
+
+typedef long long stone;
+
+typedef struct Stones {
+  stone first;
+  stone second;
+} Stones;
+
+typedef struct StonePile {
+  stone value;
+  long long count;
+} StonePile;
+
+int sort_stone_piles(const void *a, const void *b) {
+  return ((*(StonePile*) a).value - (*(StonePile*) b).value) % INT_MAX;
+}
+
+int num_digits(stone s) {
+  stone comp = 10;
+  int digits = 1;
+  while (s >= comp) {
+    digits++;
+    comp *= 10;
+  }
+  return digits;
+}
+
+int num_children(stone s, int generations_remaining) {
+  if (generations_remaining == 0) return 1;
+
+  int next_gen = generations_remaining - 1;
+  int stone_num_digits = num_digits(s);
+  int nc;
+
+  if (s == 0ll) {
+    nc = num_children(1, next_gen);
+  } else if (stone_num_digits % 2 == 0) {
+    stone comp = 10;
+    for (int i = 1; i < stone_num_digits / 2; i++) comp *= 10;
+    nc = num_children(s / comp, next_gen) + num_children(s % comp, next_gen);
+  } else {
+    nc = num_children(s * 2024, next_gen);
+  }
+  return nc;
+}
+
+Stones change(stone s) {
+  Stones stones;
+  int stone_num_digits = num_digits(s);
+
+  if (s == 0ll) {
+    stones.first = 1;
+    stones.second = -1;
+  } else if (stone_num_digits % 2 == 0) {
+    stone comp = 10;
+    for (int i = 1; i < stone_num_digits / 2; i++) comp *= 10;
+    stones.first = s / comp;
+    stones.second = s % comp;
+  } else {
+    stones.first = s * 2024;
+    stones.second = -1;
+  }
+
+  return stones;
+}
+
+int main() {
+  char *input = aoc_read_input();
+
+  StonePile stone_array[50000], next_stone_array[50000];
+  int stone_count = 0, next_stone_count = 0;
+  char *current_token = strtok(input, " ");
+
+  long long stone_count_sum = 0ll;
+  long long big_stone_count_sum = 0ll;
+
+  while (current_token != NULL) {
+    stone_array[stone_count].value = atoll(current_token);
+    stone_array[stone_count].count = 1ll;
+    stone_count++;
+    current_token = strtok(NULL, " ");
+  }
+
+  for (int i = 0; i < 75; i++) {
+    next_stone_count = 0;
+    for (int j = 0; j < stone_count; j++) {
+      Stones s = change(stone_array[j].value);
+      next_stone_array[next_stone_count].value = s.first;
+      next_stone_array[next_stone_count].count = stone_array[j].count;
+      next_stone_count++;
+      if (s.second != -1) {
+	next_stone_array[next_stone_count].value = s.second;
+	next_stone_array[next_stone_count].count = stone_array[j].count;
+	next_stone_count++;
+      }
+    }
+    qsort(next_stone_array, next_stone_count, sizeof(StonePile), sort_stone_piles);
+
+    stone_array[0].count = next_stone_array[0].count;
+    stone_array[0].value = next_stone_array[0].value;
+    stone_count = 1;
+
+    for (int j = 1; j < next_stone_count; j++) {
+      if (next_stone_array[j].value == stone_array[stone_count - 1].value) {
+	stone_array[stone_count - 1].count += next_stone_array[j].count;
+      } else {
+	stone_count++;
+	stone_array[stone_count - 1].value = next_stone_array[j].value;
+	stone_array[stone_count - 1].count = next_stone_array[j].count;
+      }
+    }
+
+    if (i == 24) {
+      stone_count_sum = 0;
+      for (int j = 0; j < stone_count; j++) {
+	stone_count_sum += stone_array[j].count;
+      }
+    }
+
+    if (i == 74) {
+      big_stone_count_sum = 0;
+      for (int j = 0; j < stone_count; j++) {
+	big_stone_count_sum += stone_array[j].count;
+      }
+    }
+  }
+
+
+  printf("Part 1: %lld\n", stone_count_sum);
+  printf("Part 2: %lld\n", big_stone_count_sum);
+  
+  aoc_free();
+  return 0;
+}