C solution for week 99, part 2

2 files changed, 94 insertions, 0 deletions

diff --git a/challenge-099/abigail/README.md b/challenge-099/abigail/README.md
index 2cf96b11c4..3e98f336de 100644
--- a/challenge-099/abigail/README.md
+++ b/challenge-099/abigail/README.md
@@ -81,6 +81,7 @@ Output: 3
 
 ### Solutions
 * [AWK](awk/ch-2.awk)
+* [C](c/ch-2.c)
 * Perl
     * [Using regular expressions](perl/ch-2.pl)
     * [Recursive counting](perl/ch-2a.pl)
diff --git a/challenge-099/abigail/c/ch-2.c b/challenge-099/abigail/c/ch-2.c
new file mode 100644
index 0000000000..9553f698ba
--- /dev/null
+++ b/challenge-099/abigail/c/ch-2.c
@@ -0,0 +1,93 @@
+# include <stdlib.h>
+# include <stdio.h>
+# include <string.h>
+
+/*
+ * See ../README.md
+ */
+
+/*
+ * Run as: cc -o ch-2.o ch-2.c; ./ch-2.o < input-file
+ */
+
+
+/*
+ * Helper method to allocate memory for a string.
+ */
+char * malloc_char (size_t size) {
+    char * string = (char *) malloc (size * sizeof (char));
+    if (string == NULL) {
+        perror (NULL);
+        exit (1);
+    }
+    return (string);
+}
+
+/*
+ * Recursively count matches:
+ *   - If either the string or the pattern is empty, there are no matches.
+ *   - Else, + count the matches if we don't match at the first character
+ *             if the string.
+ *           + if the first character of the string equals the first
+ *             character of the pattern:
+ *             o  add 1 if the pattern is just one character long
+ *             o  else, add the number of matches starting from the
+ *                then next character in the string, and the next
+ *                character in the pattern.
+ */
+int matches (char * string,  size_t string_len,
+             char * pattern, size_t pattern_len) {
+    if (string_len == 0 || pattern_len == 0) {
+        return 0;
+    }
+
+    /*
+     * Don't match at the beginning
+     */
+    int count = matches (string + 1, string_len - 1,
+                         pattern,    pattern_len);
+    if (string [0] == pattern [0]) {
+        if (pattern_len == 1) {
+            count ++;
+        }
+        else {
+            count += matches (string  + 1, string_len  - 1,
+                              pattern + 1, pattern_len - 1);
+        }
+    }
+    return count;
+}
+
+
+/*
+ * Read input from standard input, assuming one exercise per line.
+ * Each line consists of a string $S, and a pattern $T, separated
+ * by whitespace.
+ */
+int main (void) {
+    char *  line    = NULL;
+    size_t  len     = 0;
+    size_t  str_len;
+
+    while ((str_len = getline (&line, &len, stdin)) != -1) {
+        char * string;
+        char * pattern;
+
+        string  = malloc_char (str_len);
+        pattern = malloc_char (str_len);
+
+        if (sscanf (line, "%s %s", string, pattern) != 2) {
+            fprintf (stderr, "Could not parse input\n");
+            exit (1);
+        }
+
+        printf ("%d\n", matches (string,  strnlen (string,  str_len),
+                                 pattern, strnlen (pattern, str_len)));
+
+        free (pattern);
+        free (string);
+    }
+    free (line);
+
+    return (0);
+}