C code for challenge 69 task 2

Very slow for n>15 or so, so in need of some refactoring.

1 files changed, 53 insertions, 0 deletions

diff --git a/challenge-069/walt-mankowski/c/ch-2.c b/challenge-069/walt-mankowski/c/ch-2.c
new file mode 100644
index 0000000000..36f1463e32
--- /dev/null
+++ b/challenge-069/walt-mankowski/c/ch-2.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+const size_t min(const size_t a, const size_t b) {
+    return a <= b ? a : b;
+}
+
+char *rev(const char *s) {
+    const size_t len = strlen(s);
+    char *t = malloc(len+1);
+    strcpy(t, s);
+    for (size_t i = 0; i < min(len/2+1, len); i++) {
+        const size_t j = len-1-i;
+        char tmp = t[i];
+        t[i] = t[j];
+        t[j] = tmp;
+    }
+
+    return t;
+}
+
+char *swtch(char *s) {
+    for (size_t i = 0; i < strlen(s); i++)
+        if (s[i] == '0')
+            s[i] = '1';
+        else
+            s[i] = '0';
+
+    return s;
+}
+
+char *S(const int n) {
+    const size_t len = (1 << n) - 1;
+    char *s = malloc(len);
+    s[0] = '\0';
+
+    for (int i = 1; i <= n; i++) {
+        char *rs = swtch(rev(s));
+        const size_t eos = (1 << (i-1)) - 1;
+        s[eos] = '0';
+        strcat(s+eos+1, rs);
+        free(rs);
+    }
+    return s;
+}
+
+int main(int argc, char *argv[]) {
+    const int n = atoi(argv[1]);
+    puts(S(n));
+    
+    return 0;
+}