My solutions to the problems from Facebook Hackercup 2013 Qualification Round.

balanced_smileys.rb

$dp = nil

def try(l,r,s)
	case s[l]
	when '('
		((l+1)..r).each do |i|
			return true if s[i] == ')' && go(l+1,i-1,s) && go(i+1,r,s)
		end
		false
	when ':'
		go(l+1,r,s) || ( l < r && (s[l+1] == '(' || s[l+1] == ')') && go(l+2,r,s))
	when ')'
		false
	else #	when 'a'..'z', ' '
		go(l+1,r,s)
	end
end

def go(l,r,s)
	return true if l > r
	if $dp[l][r] == nil
		$dp[l][r] = try(l,r,s)
	else
		$dp[l][r]
	end
end

gets.to_i.times do |i|
	s = gets.strip
	n = s.length
	$dp = Array.new(n).map!{Array.new(n)}
	out = go(0,n-1,s) ? "YES" : "NO"
	puts "Case \##{i+1}: #{out}"
end

beautiful_strings.rb

gets.to_i.times do |i|
	s = gets.strip.downcase
	out = ('a'..'z').map{|c| s.count(c)}.sort.zip(1..26).map{|x,y| x*y}.inject(:+)
	puts "Case \##{i+1}: #{out}"
end

find_the_min.cpp

#include <iostream>
#include <set>
#include <vector>
#include <map>
using namespace std;

int main(void)
{
	int T;
	cin >> T;
	for (int C = 1; C <= T; C++)
	{
		int n, k;
		cin >> n >> k;
		long long A,b,c,r;
		cin >> A >> b >> c >> r;
		vector <int> a(2*k+2);
		set <int> S;
		map <int,int> R;
		S.insert(0);
		a[0] = (int)A;
		for (int i = 1; i < k; i++)
			a[i] = (int)(((( b * ((long long)a[i-1])) % r) + (long long)c) % r), S.insert(i);
		S.insert(k);
		for (int i = 0; i < k; i++)
			S.erase(a[i]), R[a[i]]++;
		int m = a[k-1], it;
		for (it = k; it < n && it < 2 * k + 1; it++)
		{
			m = *(S.begin());
			R[m]++;
			if ( (--R[a[it-k]]) == 0)
				S.insert(a[it-k]);
			S.erase(m);
			a[ it] = m;
		}
		cout << "Case #" << C << ": " << a[(n-1-k)%(k+1) + k ] << endl;
	}
	return 0;
}