Task: Set puzzle
C: #include <stdio.h>
#include <stdlib.h>

char *names[4][3] = {
	{ "red", "green", "purple" },
	{ "oval", "squiggle", "diamond" },
	{ "one", "two", "three" },
	{ "solid", "open", "striped" }
};

int set[81][81];

void init_sets(void)
{
	int i, j, t, a, b;
	for (i = 0; i < 81; i++) {
		for (j = 0; j < 81; j++) {
			for (t = 27; t; t /= 3) {
				a = (i / t) % 3;
				b = (j / t) % 3;
				set[i][j] += t * (a == b ? a : 3 - a - b);
			}
		}
	}
}

void deal(int *out, int n)
{
	int i, j, t, c[81];
	for (i = 0; i < 81; i++) c[i] = i;
	for (i = 0; i < n; i++) {
		j = i + (rand() % (81 - i));
		t = c[i], c[i] = out[i] = c[j], c[j] = t;
	}
}

int get_sets(int *cards, int n, int sets[][3])
{
	int i, j, k, s = 0;
	for (i = 0; i < n; i++) {
		for (j = i + 1; j < n; j++) {
			for (k = j + 1; k < n; k++) {
				if (set[cards[i]][cards[j]] == cards[k])
					sets[s][0] = i,
					sets[s][1] = j,
					sets[s][2] = k,
					s++;
			}
		}
	}

	return s;
}

void show_card(int c)
{
	int i, t;
	for (i = 0, t = 27; t; i++, t /= 3)
		printf("%9s", names[i][(c/t)%3]);
	putchar('\n');
}

void deal_sets(int ncard, int nset)
{
	int c[81];
	int csets[81][3]; 
	int i, j, s;

	do deal(c, ncard); while ((s = get_sets(c, ncard, csets)) != nset);

	printf("dealt %d cards\n", ncard);
	for (i = 0; i < ncard; i++) {
		printf("%2d:", i);
		show_card(c[i]);
	}
	printf("\nsets:\n");

	for (i = 0; i < s; i++) {
		for (j = 0; j < 3; j++) {
			printf("%2d:", csets[i][j]);
			show_card(c[csets[i][j]]);
		}
		putchar('\n');
	}
}

int main(void)
{
	init_sets();
	deal_sets(9, 4);

	while (1) deal_sets(12, 6);

	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;
    }
}