C 2024 day 2

c/2024/2/red_nosed_reports.c

@@ -0,0 +1,108 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "../../lib/aoc.h"
+
+typedef struct Report {
+  int *levels;
+  int size;
+  int skip;
+} Report;
+
+bool report_increasing(Report *report) {
+  int current = report->levels[0];
+  int i = 1;
+  if (report->skip == 0) {
+    current = report->levels[1];
+    i = 2;
+  }
+  for (; i < report->size; i++) {
+    if (i == report->skip) continue;
+    int next = report->levels[i];
+    if (next <= current) return false;
+    current = next;
+  }
+  return true;
+}
+
+bool report_decreasing(Report *report) {
+  int current = report->levels[0];
+  int i = 1;
+  if (report->skip == 0) {
+    current = report->levels[1];
+    i = 2;
+  }
+  for (; i < report->size; i++) {
+    if (i == report->skip) continue;
+    int next = report->levels[i];
+    if (next >= current) return false;
+    current = next;
+  }
+  return true;
+}
+
+bool report_changing_slowly(Report *report) {
+  int current = report->levels[0];
+  int i = 1;
+  if (report->skip == 0) {
+    current = report->levels[1];
+    i = 2;
+  }
+  for (; i < report->size; i++) {
+    if (i == report->skip) continue;
+    int next = report->levels[i];
+    if (abs(next - current) > 3) return false;
+    current = next;
+  }
+  return true;
+}
+
+bool report_safe_with_skips(Report *report) {
+  for (int i = -1; i < report->size; i++) {
+    report->skip = i;
+    if ((report_increasing(report) || report_decreasing(report)) && report_changing_slowly(report)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool report_safe(Report *report) {
+  report->skip = -1;
+  return (report_increasing(report) || report_decreasing(report)) && report_changing_slowly(report);
+}
+
+void populate_report(Report *report, char *line) {
+  report->size = 0;
+  char *level = strtok(line, " ");
+  while (level != NULL) {
+    report->levels[report->size] = atoi(level);
+    report->size++;
+    level = strtok(NULL, " ");
+  }
+}
+
+int main() {
+  char *line;
+
+  Report report;
+  report.levels = malloc(20 * sizeof(int));
+  report.size = 0;
+
+  int safe_report_count = 0;
+  int safe_skip_report_count = 0;
+
+  while ((line = aoc_read_line()) != NULL) {
+    populate_report(&report, line);
+    if (report_safe(&report)) safe_report_count += 1;
+    if (report_safe_with_skips(&report)) safe_skip_report_count += 1;
+  }
+
+  printf("Part 1: %d\n", safe_report_count);
+  printf("Part 1: %d\n", safe_skip_report_count);
+
+  aoc_free();
+  return 0;
+}