Week 2: Exercises

1. Triple List

Write a predicate triple(L) that is true if L is a list with three elements, all of which are identical.

2. Triple Diff

Write a predicate triple_diff(L) that is true if L is a list with three elements, all of which are different.

3. Second Last

Write a predicate second_last(X, L) that is true if X is the next-to-last element of L.

4. Next To

Write a predicate next_to(X, Y, L) that is true if elements X and Y appear in L, with Y immediately after X.

5. Even Length

Write a predicate even_length(L) that is true if the length of L is an even integer.

6. Longer

Write a predicate longer(L, M) that is true if L is longer than M.

7. Double Length

Write a predicate double_length(L, M) that is true if L is twice as long as M.

8. Is A List

Write a predicate is_list(L) that is true if L is a list of any length.

9. Length

Write a predicate len(L, N) that is true if the length of list L is N.

10. All Different

Write a predicate all_diff(L) that is true if all elements of L are all different.

11. Ordered List

Write a predicate ordered(L) that is true if the integers in L are in non-decreasing order.

12. Nth

Write a predicate nth(N, L, X) that is true if the nth element of list L is X, where the first element has index 0.

13. Append

Write a predicate append(L, M, N) that is true if the lists L and M can be appended to form N.

14. Reverse

Write a predicate reverse(L, M) that is true if L and M contain the same elements in reverse order.

15. Select

Write a predicate select(X, L, M) that is true if X can be removed from L to make M. Equivalently, select(X, L, M) is true if X can be inserted anywhere in M to make L.

16. Select, Extended

Write a predicate select(X, L, Y, M) that is true if L and M are identical except (possibly) for a single element, which is X in L and is Y in M.

17. Greatest Common Divisor

Write a predicate gcd(I, J, K) that is true if the greatest common divisor of I and J is K.

18. Prime

Write a predicate is_prime(N) that is true if N is prime.

19. All Primes

Write a predicate all_primes(I, J) that returns a list of all prime numbers between I and J, inclusive.

20. Smallest Prime Factor

Write a predicate smallest_factor(N, P) that is true if P is the smallest prime factor of N.

21. Subset

Write a predicate subset(L, M) that is true if M is a subset of the elements in L, with elements in the same order as they appear in L.

22. Permutations

Write a predicate permutation(L, M) that is true if the list L is a permutation of M.

23. Combinations

Write a predicate combination(L, N, M) that is true if M is a combination of N elements of L, i.e. a subset of size N that has its elements in the same order as in L. Elements in M should appear in the same order as in L.

24. Insertion Sort

Write a predicate insertion_sort(L, S) that sorts a list L of integers. Use an insertion sort.

25. Crosswords

Suppose that we'd like to fill in a 3 x 3 grid with letters so that every row and column contains one of these words:

AGE, AGO, CAN, CAR, NEW, RAN, ROW, WON

Write a Prolog program that can find all possible solutions.

26. Mini-Minesweeper

Consider the following tiny Minesweeper board of dimensions 5 x 2:

A number N means that there are N mines in adjacent squares (which may be adjacent horizontally or diagonally).

Write a Prolog program that can find all possible positions for the mines.

27. Beethoven's Wig

Someone has stolen Beethoven's wig and has put it in one of four locked boxes. The boxes are numbered 1,2,3,4 in that order. There are four different keys that each have their own color. Also:

  1. The green key goes to the third or fourth box.

  2. The wig is to the left of the fourth box.

  3. The wig is to the right of the first box.

  4. The yellow key is to the left of the wig.

  5. The blue key is to the right of the yellow key and to the left of the green key.

  6. The red key goes to the first box.

Which box contains Beethoven's wig? Write a Prolog program that can find the answer.

28. Acyclic Directed Graph

Consider this acyclic directed graph:



One way to represent a graph in Prolog is as a list of edges. For example, we can represent the graph above by this term:

G = [ [a, b], [a, e], [b, c], [b, f], [e, d],
      [e, f], [f, c], [g, d], [g, h], [h, f] ].

Write a predicate path(G, V, W, L) that is true if L is a list of vertices along a path from V to W in the graph G.