c 2024 day 7

c/2024/7/bridge_repair.c

@@ -0,0 +1,105 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "../../lib/aoc.h"
+
+typedef struct Calibration {
+  long test_value;
+  int numbers[20];
+  int number_count;
+} Calibration;
+
+void base_three(char *string, int number, int length) {
+  int i = 0;
+  for (; i < length; i++) {
+    string[length - i - 1] = (number % 3) + '0';
+    number /= 3;
+  }
+  string[length] = '\0';
+}
+
+bool true_permutation(Calibration *c, int permutation) {
+  long value = c->numbers[0];
+  for (int i = 1; i < c->number_count; i++) {
+    int operator = permutation & 1;
+    permutation >>= 1;
+    if (operator == 0) {
+      value += c->numbers[i];
+    } else {
+      value *= c->numbers[i];
+    }
+  }
+  return value == c->test_value;
+}
+
+bool true_permutation_p2(Calibration *c, char *permutation) {
+  long value = c->numbers[0];
+  for (int i = 1; i < c->number_count; i++) {
+    int operator = permutation[i - 1];
+    if (operator == '0') {
+      value += c->numbers[i];
+    } else if (operator == '1') {
+      value *= c->numbers[i];
+    } else {
+      char concat[100];
+      sprintf(concat, "%ld%ld", value, c->numbers[i]);
+      value = atol(concat);
+    }
+  }
+  return value == c->test_value;
+}
+
+bool true_calibration(Calibration *c) {
+  int permutation_count = 2 << (c->number_count - 2);
+  for (int i = 0; i < permutation_count; i++) {
+    if (true_permutation(c, i)) return true;
+  }
+  return false;
+}
+
+bool true_calibration_p2(Calibration *c) {
+  int permutation_count = 1;
+  for (int i = 1; i < c->number_count; i++) {
+    permutation_count *= 3;
+  }
+  char permutation_string[c->number_count];
+  for (int i = 0; i < permutation_count; i++) {
+    base_three(permutation_string, i, c->number_count - 1);
+    if (true_permutation_p2(c, permutation_string)) return true;
+  }
+  return false;
+}
+
+void calibration_from_line(Calibration *c, char *line) {
+  c->number_count = 0;
+  char *token = strtok(line, ":");
+  c->test_value = atol(token);
+  while(token = strtok(NULL, " ")) {
+    c->numbers[c->number_count++] = atoi(token);
+  }
+}
+
+int main() {
+  char *line;
+  Calibration c;
+
+  long long calibration_result = 0;
+  long long calibration_result_p2 = 0;
+  while((line = aoc_read_line()) != NULL) {
+    calibration_from_line(&c, line);
+    if (true_calibration(&c)) {
+      calibration_result += c.test_value;
+    }
+    if (true_calibration_p2(&c)) {
+      calibration_result_p2 += c.test_value;
+    }
+  }
+
+  printf("Part 1: %lld\n", calibration_result);
+  printf("Part 2: %lld\n", calibration_result_p2);
+
+  aoc_free();
+  return 0;
+}