Just finished TOPCODER SRM 504 DIVISION 2 competition. Solved 250 and 500 point problems.

Here are my solutions in C#

using System;

public class ComparerInator
{
    public delegate TResult Func<T1, T2, TResult>(T1 arg1, T2 arg2);
    
    public int makeProgram(int[] A, int[] B, int[] wanted)
    {
        if (test(A, B, wanted, f_a) || test(A, B, wanted, f_b))
            return 1;
        if (test(A, B, wanted, f_ab) || test(A, B, wanted, f_ba))
            return 7;
            
        return -1;
    }
    
    bool test(int[] A, int[] B, int[] wanted, Func<int, int, int> f)
    {
        for (int i=0; i < A.Length; i++)
        {
            if (f(A[i], B[i]) == wanted[i])
                continue;
                
            return false;
        }
        
        return true;
    }
    
    int f_a(int a, int b)
    {
        return a;
    }
    
    int f_b(int a, int b)
    {
        return b;
    }
    
    int f_ab(int a, int b)
    {
        return a<b?a:b;
    }
    
    int f_ba(int a, int b)
    {
        return a<b?b:a;
    }
}

using System;
using System.Text;

public class MathContest
{
    public int countBlack(String ballSequence, int repetitions)
    {
        StringBuilder sb = new StringBuilder(ballSequence.Length * repetitions);
        for (int i = 0; i < repetitions; i++)
            sb.Append(ballSequence);
            
        s = sb.ToString();
        
        pos = -1;
        invert = false;
        direction = 1;
        end = s.Length - 1;
        
        int count = 0;
        
        char ball = get_next();
        while (ball != (Char)0)
        {
            if (ball == 'B')
                count++;
            ball = get_next();
        }
        
        return count;
    }

    string s;
    int pos;
    bool invert;
    int direction;
    int end;

    char get_next()
    {
        if (pos == end)
            return (Char)0;    
            
        pos += direction;
        char ch = s[pos];
        
        if (invert)
        {
            if (ch == 'B')
                ch = 'W';
            else
                ch = 'B';
        }
        
        if (ch == 'B')
            invert = invert ? false : true;
        else
        {
            int t = end;
            end = pos + direction;
            pos = t + direction;
            direction = direction == 1 ? -1 : 1;
        }
        
        return ch;
    }
}

Unfortunately I've made a mistake in 500-point problem. Instead of

end = pos + direction;
            pos = t + direction;

I wrote

end = pos;
            pos = t;

so my solution was successfully challenged and gave me zero points.

More then it - it was my first competition on TopCoder and there was a problem running the engine. So results are not go to rating. Well... next time.