Initial commit

2020/day06/day06.c

@@ -0,0 +1,58 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <input file>\n", argv[0]);
+    return 0;
+  }
+
+  FILE *fp = fopen(argv[1], "r");
+  if (fp == NULL) {
+    printf("Could not open file %s\n", argv[1]);
+    return 1;
+  }
+
+  bool flag_newline = false;
+  unsigned int answer_count = 0;
+  unsigned int counts[26] = {0};
+  unsigned int part1 = 0;
+  unsigned int part2 = 0;
+  for (char c = getc(fp); c != EOF; c = getc(fp)) {
+    if (c == '\n' && flag_newline) {
+      for (int i = 0; i < 26; ++i) {
+        if (counts[i] > 0) {
+          part1++;
+        }
+        if (counts[i] == answer_count) {
+          part2++;
+        }
+        counts[i] = 0;
+      }
+      flag_newline = false;
+      answer_count = 0;
+    } else if (c == '\n') {
+      flag_newline = true;
+      answer_count++;
+    } else {
+      counts[c - 'a']++;
+      flag_newline = false;
+    }
+  }
+
+  for (int i = 0; i < 26; ++i) {
+    if (counts[i] > 0) {
+      part1++;
+    }
+    if (counts[i] == answer_count) {
+      part2++;
+    }
+  }
+
+  printf("%u\n", part1);
+  printf("%u\n", part2);
+
+  fclose(fp);
+  return 0;
+}