Programing Puzzles

[Wyverex]

JAnderson wrote:
> Wyverex wrote:
>> just some fun little programming puzzles I found around online...
>>
>>
>> Problem #2 Test if an int is even or odd without looping or if 
>> statement (Cant use: do, while, for, foreach, if).
>>
>> Problem #4 Find if the given number is a power of 2.
>>
>> Post Solutions to this root, comments to someones solution in that 
>> thread.
> 
> 
> Some of these are pretty standard interview questions. Although I don't 
> personally like to ask these sort of questions because they are often 
> about knowing a "trick" which you an easily lookup.  The can be fun to 
> figure out though.
> 
> Here's another common one:
> 
> | Write a bitcount for a 32-bit number.
> 
> And a little more challenging:
> 
> | Write a bitcount for a 32-bit number that is less then 15 operations 
> without using a lookup table.
> 
> | Can you do that in 12 or less?
> 
> -Joel

int count( in int i )
{
    int c = (i & 1) + (i & 2 ? 1 : 0) + (i & 4 ? 1 : 0) + (i & 8 ? 1 : 0);
    i >>= 4;
    c += (i & 1) + (i & 2 ? 1 : 0) + (i & 4 ? 1 : 0) + (i & 8 ? 1 : 0);
    i >>= 4;
    c += (i & 1) + (i & 2 ? 1 : 0) + (i & 4 ? 1 : 0) + (i & 8 ? 1 : 0);
    i >>= 4;
    c += (i & 1) + (i & 2 ? 1 : 0) + (i & 4 ? 1 : 0) + (i & 8 ? 1 : 0);

    return c;
}

int count2( in int i )
{
    int c = (i & 1) + ((i >> 1) & 1) + ((i >> 2) & 1) + ((i >> 3) & 1);
    i >>= 4;
    c += (i & 1) + ((i >> 1) & 1) + ((i >> 2) & 1) + ((i >> 3) & 1);
    i >>= 4;
    c += (i & 1) + ((i >> 1) & 1) + ((i >> 2) & 1) + ((i >> 3) & 1);
    i >>= 4;
    c += (i & 1) + ((i >> 1) & 1) + ((i >> 2) & 1) + ((i >> 3) & 1);

    return c;
}