2022: Day 6 complete

2022/6.c

@@ -0,0 +1,116 @@
+#include <stddef.h>
+#include <stdio.h>
+
+// Part 1 - finds and returns the start-of-packet marker, or 0 if none exists
+size_t get_pkt_mark(FILE *file) {
+
+  size_t pos = 0;
+  int c = 0, c_arr[4] = {0};
+
+  while ((c = fgetc(file)) != EOF) {
+
+    if (pos < 4) {
+      c_arr[pos] = c;
+      pos++;
+      continue;
+    }
+
+    int invalid_marker = 0;
+    size_t len = sizeof c_arr / sizeof *c_arr;
+    for (size_t i = 0; i < len - 1; i++) {
+      for (size_t j = i + 1; j < len; j++) {
+        if (c_arr[i] == c_arr[j]) {
+          invalid_marker = 1;
+        }
+      }
+    }
+
+    if (!invalid_marker) {
+      return pos;
+    }
+
+    c_arr[0] = c_arr[1];
+    c_arr[1] = c_arr[2];
+    c_arr[2] = c_arr[3];
+    c_arr[3] = c;
+    pos++;
+  }
+  return 0;
+}
+
+size_t get_msg_mark(FILE *file) {
+
+  size_t pos = 0;
+  int c = 0, c_arr[14] = {0};
+
+  while ((c = fgetc(file)) != EOF) {
+
+    if (pos < 14) {
+      c_arr[pos] = c;
+      pos++;
+      continue;
+    }
+
+    int invalid_marker = 0;
+    size_t len = sizeof c_arr / sizeof *c_arr;
+    for (size_t i = 0; i < len - 1; i++) {
+      for (size_t j = i + 1; j < len; j++) {
+        if (c_arr[i] == c_arr[j]) {
+          invalid_marker = 1;
+        }
+      }
+    }
+
+    if (!invalid_marker) {
+      return pos;
+    }
+
+    for (size_t i = 0; i < len - 1; i++) {
+      c_arr[i] = c_arr[i + 1];
+    }
+    c_arr[len - 1] = c;
+    pos++;
+  }
+  return 0;
+}
+
+int main(int argc, char *argv[]) {
+
+  if (argc != 2) {
+    fprintf(stderr, "USAGE: %s input_file\n", argv[0]);
+    return 1;
+  }
+
+  // Part 1 - find the start-of-packet marker
+  FILE *file = fopen(argv[1], "r");
+  if (!file) {
+    perror("fopen part1");
+    return 1;
+  }
+
+  size_t pkt_mark = get_pkt_mark(file);
+  if (!pkt_mark) {
+    fprintf(stderr, "Start-of-Packet marker not found\n");
+  } else {
+    printf("Part 1: Start-of-Packet marker at position %lu\n", pkt_mark);
+  }
+
+  fclose(file);
+
+  // Part 2 - find the start-of-message marker
+  file = fopen(argv[1], "r");
+  if (!file) {
+    perror("fopen part2");
+    return 1;
+  }
+
+  size_t msg_mark = get_msg_mark(file);
+  if (!msg_mark) {
+    fprintf(stderr, "Start-of-Message marker not found\n");
+  } else {
+    printf("Part 2: Start-of-Message marker at position %lu\n", msg_mark);
+  }
+
+  fclose(file);
+  return 0;
+}

2022/6.txt

@@ -0,0 +1 @@
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