Task: Set puzzle
C++: #include <time.h>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>

enum color {
    red, green, purple 
};
enum symbol {
    oval, squiggle, diamond 
};
enum number {
    one, two, three 
};
enum shading {
    solid, open, striped 
};
class card {
public:
    card( color c, symbol s, number n, shading h ) {
        clr = c; smb = s; nbr = n; shd = h;
    }
    color getColor() { 
        return clr;
    }
    symbol getSymbol() { 
        return smb; 
    }
    number getNumber() {
        return nbr; 
    }
    shading getShading() {
        return shd;
    }
    std::string toString() {
        std::string str = "[";
        str += clr == red ? "red " : clr == green ? "green " : "purple ";
        str += nbr == one ? "one " : nbr == two ? "two " : "three ";
        str += smb == oval ? "oval " : smb == squiggle ? "squiggle " : "diamond ";
        str += shd == solid ? "solid" : shd == open ? "open" : "striped";
        return str + "]";
    }
private:
    color    clr;
    symbol   smb;
    number   nbr;
    shading  shd;
};
typedef struct {
    std::vector<size_t> index;
} set;
class setPuzzle {
public:
    setPuzzle() {
        for( size_t c = red; c <= purple; c++ ) {
            for( size_t s = oval; s <= diamond; s++ ) {
                for( size_t n = one; n <= three; n++ ) {
                    for( size_t h = solid; h <= striped; h++ ) {
                        card crd( static_cast<color>  ( c ), 
                                  static_cast<symbol> ( s ), 
                                  static_cast<number> ( n ), 
                                  static_cast<shading>( h ) );
                        _cards.push_back( crd );
                    }
                }
            }
        }
    }
    void create( size_t countCards, size_t countSets, std::vector<card>& cards, std::vector<set>& sets ) {
        while( true ) {
            sets.clear();
            cards.clear();
            std::random_shuffle( _cards.begin(), _cards.end() );
            for( size_t f = 0; f < countCards; f++ ) {
                cards.push_back( _cards.at( f ) );
            }
            for( size_t c1 = 0; c1 < cards.size() - 2; c1++ ) {
                for( size_t c2 = c1 + 1; c2 < cards.size() - 1; c2++ ) {
                    for( size_t c3 = c2 + 1; c3 < cards.size(); c3++ ) {
                        if( testSet( &cards.at( c1 ), &cards.at( c2 ), &cards.at( c3 ) ) ) {
                            set s;
                            s.index.push_back( c1 ); s.index.push_back( c2 ); s.index.push_back( c3 );
                            sets.push_back( s );
                        }
                    }
                }
            }
            if( sets.size() == countSets ) return;
        }
    }
private:
    bool testSet( card* c1, card* c2, card* c3 ) {
        int
        c = ( c1->getColor()   + c2->getColor()   + c3->getColor()   ) % 3,
        s = ( c1->getSymbol()  + c2->getSymbol()  + c3->getSymbol()  ) % 3,
        n = ( c1->getNumber()  + c2->getNumber()  + c3->getNumber()  ) % 3,
        h = ( c1->getShading() + c2->getShading() + c3->getShading() ) % 3;
        return !( c + s + n + h );
    }
    std::vector<card> _cards;
};
void displayCardsSets( std::vector<card>& cards, std::vector<set>& sets ) {
    size_t cnt = 1;
    std::cout << " ** DEALT " << cards.size() << " CARDS: **\n";
    for( std::vector<card>::iterator i = cards.begin(); i != cards.end(); i++ ) {
        std::cout << std::setw( 2 ) << cnt++ << ": " << ( *i ).toString() << "\n";
    }
    std::cout << "\n ** CONTAINING " << sets.size() << " SETS: **\n";
    for( std::vector<set>::iterator i = sets.begin(); i != sets.end(); i++ ) {
        for( size_t j = 0; j < ( *i ).index.size(); j++ ) {
            std::cout << " " << std::setiosflags( std::ios::left ) << std::setw( 34 ) 
                      << cards.at( ( *i ).index.at( j ) ).toString() << " : "
                      << std::resetiosflags( std::ios::left ) << std::setw( 2 ) << ( *i ).index.at( j ) + 1 << "\n";
        }
        std::cout << "\n";
    }
    std::cout << "\n\n";
}
int main( int argc, char* argv[] ) {
    srand( static_cast<unsigned>( time( NULL ) ) );
    setPuzzle p;
    std::vector<card> v9, v12;
    std::vector<set>  s4, s6;
    p.create(  9, 4,  v9, s4 );
    p.create( 12, 6, v12, s6 );
    displayCardsSets(  v9, s4 );
    displayCardsSets( v12, s6 );
    return 0;
}

Java: import java.util.*;

public class SetPuzzle {

    enum Color {

        GREEN(0), PURPLE(1), RED(2);

        private Color(int v) {
            val = v;
        }
        public final int val;
    }

    enum Number {

        ONE(0), TWO(1), THREE(2);

        private Number(int v) {
            val = v;
        }
        public final int val;
    }

    enum Symbol {

        OVAL(0), DIAMOND(1), SQUIGGLE(2);

        private Symbol(int v) {
            val = v;
        }
        public final int val;
    }

    enum Fill {

        OPEN(0), STRIPED(1), SOLID(2);

        private Fill(int v) {
            val = v;
        }
        public final int val;
    }

    private static class Card implements Comparable<Card> {

        Color c;
        Number n;
        Symbol s;
        Fill f;

        @Override
        public String toString() {
            return String.format("[Card: %s, %s, %s, %s]", c, n, s, f);
        }

        @Override
        public int compareTo(Card o) {
            return (c.val - o.c.val) * 10 + (n.val - o.n.val);
        }
    }
    private static Card[] deck;

    public static void main(String[] args) {
        deck = new Card[81];
        Color[] colors = Color.values();
        Number[] numbers = Number.values();
        Symbol[] symbols = Symbol.values();
        Fill[] fillmodes = Fill.values();
        for (int i = 0; i < deck.length; i++) {
            deck[i] = new Card();
            deck[i].c = colors[i / 27];
            deck[i].n = numbers[(i / 9) % 3];
            deck[i].s = symbols[(i / 3) % 3];
            deck[i].f = fillmodes[i % 3];
        }
        findSets(12);
    }

    private static void findSets(int numCards) {
        int target = numCards / 2;
        Card[] cards;
        Card[][] sets = new Card[target][3];
        int cnt;
        do {
            Collections.shuffle(Arrays.asList(deck));
            cards = Arrays.copyOfRange(deck, 0, numCards);
            cnt = 0;

            outer:
            for (int i = 0; i < cards.length - 2; i++) {
                for (int j = i + 1; j < cards.length - 1; j++) {
                    for (int k = j + 1; k < cards.length; k++) {
                        if (validSet(cards[i], cards[j], cards[k])) {
                            if (cnt < target)
                                sets[cnt] = new Card[]{cards[i], cards[j], cards[k]};
                            if (++cnt > target) {
                                break outer;
                            }
                        }
                    }
                }
            }
        } while (cnt != target);

        Arrays.sort(cards);

        System.out.printf("GIVEN %d CARDS:\n\n", numCards);
        for (Card c : cards) {
            System.out.println(c);
        }
        System.out.println();

        System.out.println("FOUND " + target + " SETS:\n");
        for (Card[] set : sets) {
            for (Card c : set) {
                System.out.println(c);
            }
            System.out.println();
        }
    }

    private static boolean validSet(Card c1, Card c2, Card c3) {
        int tot = 0;
        tot += (c1.c.val + c2.c.val + c3.c.val) % 3;
        tot += (c1.n.val + c2.n.val + c3.n.val) % 3;
        tot += (c1.s.val + c2.s.val + c3.s.val) % 3;
        tot += (c1.f.val + c2.f.val + c3.f.val) % 3;
        return tot == 0;
    }
}