On Wednesday, 26 June 2013 at 20:51:35 UTC, Gary Willoughby wrote:
Just for a bit of fun, I saw this question posted on reddit the
other day and wondered how *you* would solve this in D?
http://stackoverflow.com/questions/731832/interview-question-ffn-n
The question is ambiguous as to what they mean by -n. Do they
mean the result of negation on the 32bit signed int, or do they
mean the negative of the number represented by that int. this
matters because -int.min evaluates to int.min due to wraparound.
So.. If we assume we want the proper mathematical negation:
Taking note that although the spec specifies n as a 32bit integer
it says nothing about the signature of the function or the type
of the result, we can just use implicit int->long
byte s(long n)
{
return (n & 0x8000000000000000) ? -1 : 1;
}
long f(long x)
{
if(x == 0) return 0;
if(x % 2) return x + s(x);
return s(x) - x;
}
unittest
{
foreach(int n; int.min + 1 .. int.max)
{
assert(f(f(n)) == -n);
}
assert(f(f(int.max)) == -int.max);
}
