C solution for week 114, part 1

2 files changed, 98 insertions, 0 deletions

diff --git a/challenge-114/abigail/README.md b/challenge-114/abigail/README.md
index 317c387333..ba6d2722ec 100644
--- a/challenge-114/abigail/README.md
+++ b/challenge-114/abigail/README.md
@@ -18,6 +18,7 @@ Output: 1001
 ### Solutions
 * [AWK](awk/ch-1.awk)
 * [Bash](bash/ch-1.sh)
+* [C](c/ch-1.c)
 * [Perl](perl/ch-1.pl)
 
 ### Blog
diff --git a/challenge-114/abigail/c/ch-1.c b/challenge-114/abigail/c/ch-1.c
new file mode 100644
index 0000000000..798f875954
--- /dev/null
+++ b/challenge-114/abigail/c/ch-1.c
@@ -0,0 +1,97 @@
+# include <stdlib.h>
+# include <stdio.h>
+# include <string.h>
+# include <stdbool.h>
+
+/*
+ * See ../README.md
+ */
+
+/*
+ * Run as: cc -o ch-1.o ch-1.c; ./ch-1.o < input-file
+ */
+
+int main (void) {
+    char *  line    = NULL;
+    size_t  len     = 0;
+    size_t  str_len;
+
+    while ((str_len = getline (&line, &len, stdin)) != -1) {
+        char * line_ptr = line;
+        str_len --;   /* Don't care about newline. */
+        /*
+         * Do we have just 9s?
+         */
+        bool all_nines = true;
+        for (size_t i = 0; i < str_len; i ++) {
+            if (line [i] != '9') {
+                all_nines = false;
+                break;
+            }
+        }
+        if (all_nines) {
+            printf ("1");
+            for (size_t i = 0; i < str_len - 1; i ++) {
+                printf ("0");
+            }
+            printf ("1\n");
+            continue;
+        }
+
+        /*
+         * Single character?
+         */
+        if (str_len == 1) {
+            line [0] ++;
+            printf ("%s", line);
+            continue;
+        }
+
+        size_t mid = str_len / 2;
+
+        /*
+         * Is the first part reversed greater than the last part?
+         */
+        bool is_greater = false;
+        ssize_t i;
+        size_t j;
+        for (i = mid - 1, j = mid + (str_len & 1); i >= 0; i --, j ++) {
+            if (line [i] > line [j]) {
+                is_greater = true;
+                break;
+            }
+            if (line [i] < line [j]) {
+                break;
+            }
+        }
+        /*
+         * If not greater, we need to add one of the first part (including
+         * the middle part). We do this by starting from the middle, turning
+         * 9s into 0s, and adding 1 to something not a 9. In the latter
+         * case, we terminate the loop.
+         */
+        if (!is_greater) {
+            for (i = mid - 1 + (str_len & 1); i >= 0; i --) {
+                if (line [i] == '9') {
+                    line [i] = '0';
+                }
+                else {
+                    line [i] ++;
+                    break;
+                }
+            }
+        }
+
+        /*
+         * Now, copy the first half to the second; reversed
+         */
+        for (i = mid - 1, j = mid + (str_len & 1); i >= 0; i --, j ++) {
+            line [j] = line [i];
+        }
+
+        printf ("%s", line);
+    }
+    free (line);
+
+    return (0);
+}