feat(solutions): add a-phone-code/c/function

challenges/a-phone-code/solutions/c/function/README.md

@@ -0,0 +1,3 @@
+# a-phone-code/c/function
+
+Created by [@theoludwig](https://github.com/theoludwig) on 13 May 2025.

challenges/a-phone-code/solutions/c/function/character.c

@@ -0,0 +1,7 @@
+#include "character.h"
+
+void character_append(char* string, char character) {
+  size_t length = strlen(string);
+  string[length] = character;
+  string[length + 1] = '\0';
+}

challenges/a-phone-code/solutions/c/function/character.h

@@ -0,0 +1,16 @@
+#ifndef __CHARACTER__
+#define __CHARACTER__
+
+#include <stdlib.h>
+#include <string.h>
+
+/**
+ * @brief Append a character to a string, assuming string points to an array
+ * with enough space.
+ *
+ * @param string
+ * @param character
+ */
+void character_append(char* string, char character);
+
+#endif

challenges/a-phone-code/solutions/c/function/input.c

@@ -0,0 +1,14 @@
+#include "input.h"
+
+char* input() {
+  char character;
+  size_t length = 1;
+  char* string = malloc(length * sizeof(char));
+  *string = '\0';
+  while ((character = getchar()) != '\n' && character != EOF) {
+    length++;
+    string = realloc(string, length * sizeof(char));
+    character_append(string, character);
+  }
+  return string;
+}

challenges/a-phone-code/solutions/c/function/input.h

@@ -0,0 +1,16 @@
+#ifndef __INPUT__
+#define __INPUT__
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "character.h"
+
+/**
+ * @brief Read a line from stdin.
+ *
+ * @return char*
+ */
+char* input();
+
+#endif

challenges/a-phone-code/solutions/c/function/solution.c

@@ -0,0 +1,40 @@
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "input.h"
+
+int main() {
+  size_t count = (size_t)atoi(input());
+  size_t prefix_length = 0;
+
+  char* last = NULL;
+  for (size_t i = 1; i < count; i++) {
+    if (last == NULL) {
+      last = input();
+    }
+    char* current = input();
+
+    size_t prefix_current_length = 0;
+    for (size_t j = 0; j < strlen(current); j++) {
+      if (current[j] == last[j]) {
+        prefix_current_length += 1;
+      } else {
+        break;
+      }
+    }
+
+    if (prefix_length > prefix_current_length) {
+      prefix_length = prefix_current_length;
+    } else if (prefix_length == 0) {
+      prefix_length = prefix_current_length;
+    }
+
+    last = current;
+  }
+
+  printf("%ld\n", prefix_length);
+  return EXIT_SUCCESS;
+}