When Reversing the Interview Process becomes How Would You Do Fun Things in C

My boss’s boss’s pals wrote this: http://blog.exodusintel.com/2012/09/18/reversing-the-interview-process/

Its a story about how someone was asked a crazy fun C question in an interview and how the new team decided to try it.

After reading this and discussing it with coworkers, I decided to try it and of course the first thing that came to my mind was a way to use tail recursion to do it.

 1 #include <stdio.h>
 2 
 3 int c;
 4 //auto func0 = [&] () -> int { c++; _strlen(s+1);};
 5 //auto funcn = [&] () -> int { return c; };
 6 int rs(char* s);
 7 int go(char* s) { c++; return rs(s+1); }
 8 int ret(char* s) { return c; }
 9 int rs(char* s) {
10     int (*func[2]) (char *s) = {ret,go};
11     char i = (*s>>7 | *s>>6 | *s>>5 | *s>>4 | 
        *s>>3 | *s>>2 | *s>>1) & 1;
12     return func[i](s);
13 }
14 int _strlen(char* s) {
15     c = 0;
16     return rs(s);
17 }
18 
19 int main(int argc, char* argv[]) {
20     printf("_strlen(%s): %d\n", argv[1], 
        _strlen(argv[1]));
21     return 0;
22 }

After writing it, I went and looked at the other fella solutions for the second time. I should also mention that I haven’t written C on the job in 11 years, and when I did then, it was one tiny program which was quickly replaced with perl. I have never been anything other than an intro beginner C programmer.

Things I noticed after going back is that my solution is somewhat similar to Brandon and Zef’s solution, but I think both my use of function pointers and bit shifting are more elementary. I’m still not sure about how some parts of their solution works.