feat(solutions): add first-non-repeating-character/c/function

challenges/first-non-repeating-character/solutions/c/function/README.md

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+# first-non-repeating-character/c/function
+
+Created by [@Divlo](https://github.com/Divlo) on 8 October 2021.

challenges/first-non-repeating-character/solutions/c/function/character.c

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

challenges/first-non-repeating-character/solutions/c/function/character.h

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+#ifndef CHARACTER_H
+#define CHARACTER_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/first-non-repeating-character/solutions/c/function/input.c

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+#include "input.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "character.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/first-non-repeating-character/solutions/c/function/input.h

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+#ifndef INPUT_H
+#define INPUT_H
+
+/**
+ * @brief Read a line from stdin.
+ *
+ * @return char*
+ */
+char* input();
+
+#endif

challenges/first-non-repeating-character/solutions/c/function/solution.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "character.h"
+#include "input.h"
+#include "string.h"
+
+int main() {
+  char* string = input();
+  char character = string_first_non_repeating_character(string);
+  if (character == 0) {
+    printf("\n");
+  } else {
+    printf("%c\n", character);
+  }
+  free(string);
+  return EXIT_SUCCESS;
+}

challenges/first-non-repeating-character/solutions/c/function/string.c

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+#include "string.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "character.h"
+
+size_t string_total_occurrences_of_character(char* string, char character) {
+  size_t result = 0;
+  size_t string_length = strlen(string);
+  for (size_t index = 0; index < string_length; index++) {
+    char current_character = string[index];
+    if (current_character == character) {
+      result += 1;
+    }
+  }
+  return result;
+}
+
+char string_first_non_repeating_character(char* string) {
+  size_t string_length = strlen(string);
+  char result = ""[0];
+  for (size_t index = 0; index < string_length; index++) {
+    char character = string[index];
+    if (string_total_occurrences_of_character(string, character) == 1) {
+      result = character;
+      break;
+    }
+  }
+  return result;
+}

challenges/first-non-repeating-character/solutions/c/function/string.h

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+#ifndef STRING_H
+#define STRING_H
+
+#include <stdlib.h>
+
+/**
+ * @brief Returns the total number of occurrences of the given character in the string.
+ *
+ * @param string
+ * @param character
+ * @return size_t
+ */
+size_t string_total_occurrences_of_character(char* string, char character);
+
+/**
+ * @brief Returns the first non-repeating character in the given string.
+ *
+ * @param string
+ * @return char*
+ */
+char string_first_non_repeating_character(char* string);
+
+#endif