added a little string combination util because i needed it

1 files changed, 67 insertions, 0 deletions

diff --git a/combinations.c b/combinations.c
new file mode 100644
index 0000000..680c95c
--- /dev/null
+++ b/combinations.c
@@ -0,0 +1,67 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+
+void swap(char *a, char *b);
+void permute(char *s, int l, int r);
+unsigned long long fact(int n);
+
+const char red[] = "\033[31m";
+const char white[] = "\033[37m";
+const char norm[] = "\033[0m";
+
+int main(int argc, char **argv) {
+    if (argc != 2) {
+        printf("%scmb%s>%s at least give me a string :(\n", red, white, norm);
+        return 1;
+    }
+    
+    char warn = 'n';
+    char *str = strdup(argv[1]);
+    
+    unsigned long long iter_num = fact(strlen(str));
+
+    printf("%scmb%s>%s iteration count: %ld! = %llu\n", red, white, norm, strlen(str), iter_num);
+    
+    if (strlen(str) >= 6) {
+        printf("%scmb%s>%s warning, your string is >= 6 characters long.\n", red, white, norm);
+        printf("%scmb%s>%s the output %s*will*%s be %shuge%s, continue? (y/n)\n? ", red, white, norm, red, norm, red, norm);
+        scanf(" %c", &warn);
+        if (warn == 'n') {
+            printf("%scmb%s>%s quitting gracefully..\n", red, white, norm);
+            free(str);
+            return 1;
+        }
+    }
+
+    printf("%scmb%s>%s ", red, white, norm); // without \n -> prints the given string, *wink* *wink* :)
+    permute(str, 0, strlen(str) - 1);
+
+    free(str);
+    return 0;
+}
+
+void swap(char *a, char *b) {
+    char tmp = *a;
+    *a = *b;
+    *b = tmp;
+}
+
+void permute(char *s, int l, int r) {
+    if (l == r) {
+        printf("%s\n", s);
+        return;
+    }
+
+    for (int i = l; i <= r; i++) {
+        swap(&s[l], &s[i]); 
+        permute(s, l + 1, r);
+        swap(&s[l], &s[i]); 
+    }
+}
+
+unsigned long long fact(int n) {
+    return (n <= 1) ? 1 : n * fact(n - 1);
+}
+