[REFACTOR] [Hacker Rank] Warmup: Time Conversion solved ✅.

+ safer version
+ coverage increased.

Author: Gonzalo Diaz

src/lib/exercises/include/exercises/hackerrank/warmup/time_conversion.h

@@ -3,6 +3,12 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
+
+char *HACKERRANK_WARMUP_getStringFragment(const char *s, unsigned long len,
+                                          unsigned long from, unsigned long to);
+char *HACKERRANK_WARMUP_getFirst(const char *s, unsigned long n);
+char *HACKERRANK_WARMUP_getLast(const char *s, unsigned long n);
+
 char *HACKERRANK_WARMUP_firstN(const char *s, unsigned long n);
 char *HACKERRANK_WARMUP_lastN(const char *s, unsigned long n);
 

src/lib/exercises/src/hackerrank/warmup/time_conversion.c

@@ -8,76 +8,74 @@
 #include <stdlib.h>
 #include <string.h>
 
-char *HACKERRANK_WARMUP_firstN(const char *s, unsigned long n) {
-  unsigned long len = strlen(s);
-  if (n > len) {
-    return NULL;
-  }
-  if (n == 0) {
-    return NULL;
-  }
-
-  char *result = (char *)malloc((n + 1) * sizeof(char));
-  if (result == NULL) {
-    return NULL;
-  }
-
-  strncpy(result, s, n);
-
-  result[n] = '\0';
-
-  return result;
+char *HACKERRANK_WARMUP_getFirst(const char *s, unsigned long n) {
+  return HACKERRANK_WARMUP_getStringFragment(s, strlen(s), 0, n);
 }
 
-char *HACKERRANK_WARMUP_lastN(const char *s, unsigned long n) {
+char *HACKERRANK_WARMUP_getLast(const char *s, unsigned long n) {
   unsigned long len = strlen(s);
-  if (n > len) {
+  return HACKERRANK_WARMUP_getStringFragment(s, len, len - n, n);
+}
+
+char *HACKERRANK_WARMUP_getStringFragment(const char *s, unsigned long len,
+                                          unsigned long from,
+                                          unsigned long to) {
+  if (to > len) {
     return NULL;
   }
-  if (n == 0) {
+  if (to == 0) {
     return NULL;
   }
 
-  char *result = (char *)malloc((n + 1) * sizeof(char));
+  char *result = (char *)malloc((to + 1) * sizeof(char));
   if (result == NULL) {
     return NULL;
   }
 
-  strncpy(result, s + len - n, n);
+  strncpy(result, s + from, to);
 
-  result[n] = '\0';
+  result[to] = '\0';
 
   return result;
 }
 
 char *HACKERRANK_WARMUP_timeConversion(const char *s) {
-  char *meridian = HACKERRANK_WARMUP_lastN(s, 2);
+  if (s == NULL) {
+    return NULL;
+  }
+
+  char *meridian = HACKERRANK_WARMUP_getLast(s, 2);
+  char *hour_str = HACKERRANK_WARMUP_getFirst(s, 2);
 
-  char *hour_str = HACKERRANK_WARMUP_firstN(s, 2);
-  char *time_str = (char *)malloc((strlen(s) + 1) * sizeof(char));
+  size_t s_len = strlen(s);
+  char *time_str = malloc(s_len + 1);
   if (time_str == NULL) {
-    free(hour_str);
     free(meridian);
+    free(hour_str);
     return NULL;
   }
-  strcpy(time_str, s);
-  char *temp_time_str = HACKERRANK_WARMUP_lastN(time_str, strlen(time_str) - 2);
-  free(time_str);
-  time_str = temp_time_str;
-  temp_time_str = HACKERRANK_WARMUP_firstN(time_str, strlen(time_str) - 2);
-  free(time_str);
-  time_str = temp_time_str;
+
+  strncpy(time_str, s, s_len + 1);
+  char *temp_time_str;
+  unsigned long time_str_len = strlen(time_str);
+  temp_time_str = HACKERRANK_WARMUP_getLast(time_str, time_str_len - 2);
+  strncpy(time_str, temp_time_str, time_str_len - 2);
+  time_str[time_str_len - 2] = '\0';
+  free(temp_time_str);
+  temp_time_str = HACKERRANK_WARMUP_getFirst(time_str, time_str_len - 2);
+  strncpy(time_str, temp_time_str, time_str_len - 2);
+  time_str[time_str_len - 2] = '\0';
+  free(temp_time_str);
 
   char *endptr;
   long hour = strtol(hour_str, &endptr, 10);
 
   if (*endptr != '\0') {
     printf("Conversion error, non-convertible part: %s\n", endptr);
 
-    free(hour_str);
     free(meridian);
+    free(hour_str);
     free(time_str);
-    free(endptr);
     return NULL;
   } else {
     printf("The integer value is: %ld\n", hour);
@@ -94,8 +92,8 @@ char *HACKERRANK_WARMUP_timeConversion(const char *s) {
   char *conversion = malloc(BUFFER_MAX_SIZE * sizeof(char));
 
   snprintf(conversion, BUFFER_MAX_SIZE, "%02ld%s", hour, time_str);
-  free(hour_str);
   free(meridian);
+  free(hour_str);
   free(time_str);
 
   return conversion;

src/tests/unit/lib/hackerrank/warmup/time_conversion.test.cpp

@@ -34,9 +34,15 @@ TEST_CASE("time_conversion JSON Test Cases",
 
 TEST_CASE("time_conversion helper functions edge cases",
           "[hackerrank] [helper] [warmup]") {
-  CHECK(HACKERRANK_WARMUP_firstN("", 10) == nullptr);
-  CHECK(HACKERRANK_WARMUP_lastN("", 10) == nullptr);
+  // CHECK(HACKERRANK_WARMUP_getFirst(nullptr, 0) == nullptr);
 
-  CHECK(HACKERRANK_WARMUP_firstN("", 0) == nullptr);
-  CHECK(HACKERRANK_WARMUP_lastN("", 0) == nullptr);
+  CHECK(HACKERRANK_WARMUP_getFirst("", 10) == nullptr);
+  CHECK(HACKERRANK_WARMUP_getLast("", 10) == nullptr);
+
+  CHECK(HACKERRANK_WARMUP_getFirst("", 0) == nullptr);
+  CHECK(HACKERRANK_WARMUP_getLast("", 0) == nullptr);
+}
+
+TEST_CASE("time_conversion edge cases", "[hackerrank] [helper] [warmup]") {
+  CHECK(HACKERRANK_WARMUP_timeConversion("aa:bb:ccXM") == nullptr);
 }