Day 4 complete

2022/4.c

@@ -0,0 +1,90 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Assignment {
+  char *range;
+  int start;
+  int end;
+};
+
+// Split each line into 2 strings representing the assignment range for each elf
+void parse_assignments(char *assignments, struct Assignment *elf1,
+                       struct Assignment *elf2) {
+
+  elf1->range = strtok(assignments, ",");
+  elf2->range = strtok(NULL, ",");
+}
+
+// Split each assignment range into a start and end
+void parse_sections(struct Assignment *elf) {
+  elf->start = atoi(strtok(elf->range, "-,"));
+  elf->end = atoi(strtok(NULL, "-,"));
+}
+
+// Count the number of assignments that fully contain the other
+void count_subsets(int *count, struct Assignment *elf1,
+                   struct Assignment *elf2) {
+
+  if ((elf1->start >= elf2->start && elf1->end <= elf2->end) ||
+      (elf2->start >= elf1->start && elf2->end <= elf1->end)) {
+    *count += 1;
+  }
+}
+
+// Count the number of assignments with any overlapping sections
+void count_overlaps(int *count, struct Assignment *elf1,
+                    struct Assignment *elf2) {
+
+  if ((elf1->start <= elf2->end && elf1->end >= elf2->start) ||
+      (elf2->start <= elf1->end && elf2->end >= elf1->start)) {
+    *count += 1;
+  }
+}
+
+int main(int argc, char *argv[]) {
+
+  if (argc != 2) {
+    fprintf(stderr, "USAGE: %s input_file\n", argv[0]);
+    return 1;
+  }
+
+  FILE *file = fopen(argv[1], "r");
+  if (!file) {
+    perror("fopen");
+    return 1;
+  }
+
+  int part1_count = 0;
+  int part2_count = 0;
+  char assignments[16] = {0};
+
+  while (fgets(assignments, sizeof assignments / sizeof *assignments, file)) {
+
+    if (strlen(assignments) == 1) {
+      break;
+    }
+
+    struct Assignment elf1;
+    struct Assignment elf2;
+
+    assignments[strlen(assignments) - 1] = '\0';
+
+    // split input into starting and ending points
+    parse_assignments(assignments, &elf1, &elf2);
+    parse_sections(&elf1);
+    parse_sections(&elf2);
+
+    // Part 1 - count sections that fully are fully contained by another
+    count_subsets(&part1_count, &elf1, &elf2);
+
+    // Part 2 - count all overlapping sections
+    count_overlaps(&part2_count, &elf1, &elf2);
+  }
+
+  printf("Part 1 - %d ranges fully contain another\n", part1_count);
+  printf("part 2 - %d assignments overlap\n", part2_count);
+
+  fclose(file);
+  return 0;
+}