Basic Prolog (List)

1.      How to find last element from a list

Code:

lastelement([A],A).

lastelement([_|A],B):- lastelement(A,B).

Output:

lastelement([a,b,c,d],X).

X = d .

2.      How to find n^th element of a list

Code:

element_at(X,[X|_],1).

element_at(X,[_|T],Y):- element_at(X,T,Y1), Y is Y1+1.

Output:

element_at(X,[a,b,c,d],2).

X = b .

3.      How to check whether the element available or not

Code:

mem([X|_],X).

mem([_|T],X):- mem(T,X).

Output:

mem([a,b,c,d],a).

true . 

4.      How to print all members

Code:

mem([X|_],X).

mem([_|T],X):- mem(T,X).

Output:

mem([a,b,c,d],X).

X = a ;

X = b ;

X = c ;

X = d ;

false.

There is a “Prolog” keyword to find member of list. We can use it directly.

4.1. ?- member(X,[a,b,c,d]).

X = a ;

X = b ;

X = c ;

X = d.

4.2. ?- member(b,[a,b,c,d]).

True

5.      How to find the length of the list

Code:

list_length([],0).

list_length([_|T],X):- list_length(T,X1),X is X1+1.

Output:

list_length([a,b,c,d],X).

X = 4.

There is a “Prolog” keyword to find the length of the list. We can use it directly.

5.1. ?- length([a,b,c,d],X).

X = 4.

6.      How to find the sum of the integer list

Code:

sumlist([],0).

sumlist([F|R],Sum):- sumlist(R,Sum1),Sum is F+Sum1.

Output:

sumlist([12,2,4],X).

X = 18.

7.      How to find minimum number of the list

Code:

minimum([X],X).

minimum([X|Xs], X) :- minimum(Xs, Y), X < Y.

minimum([X|Xs], Y) :- minimum(Xs, Y), X >= Y.

Output:

minimum([12,2,4,5],X).

X = 2 .

8.      How to find maximum number of the list

Code:

maximum([X],X).

maximum([X|Xs], X) :- maximum(Xs, Y), X > Y.

maximum([X|Xs], Y) :- maximum(Xs, Y), X =< Y.

Output:

maximum([2,4,5,12],X).

X = 12 .

9.      How to check whether the list is palindrome or not

Code:

Palindrome(L):- reverse(L,L).

Output:

Palindrome ([l,e,v,e,l]).

true.

In here, “reverse” is a keyword.

10.   How to implement Tower of Hanoi using Prolog

Code:

move(1,X,Y,_):-

               write('Move top disk '),

               write(X),

               write(' to '),

               write(Y),

               nl.

move(N,X,Y,Z):-

               N>1,

               M is N-1,

               move(M,X,Z,Y),

               move(1,X,Y,Z),

               move(M,Z,Y,X). 

               Output:

               move(3,'S','T','A').

Move top disk S to T

Move top disk S to A

Move top disk T to A

Move top disk S to T

Move top disk A to S

Move top disk A to T

Move top disk S to T

true .

11.   How to check if the given number is odd or even

Code:

odd(X):- 1 is mod(X,2).

even(X):- 0 is mod(X,2).

Output:

?- odd(12).

false.

?- odd(1).

true.

?- even(12).

true.

?- even(9).

false.

12.   How to check max number and min number

12.1.                   Max number

Code:

max(X,Y,X):- X>=Y.

max(X,Y,Y):- Y>X.

Output:

max(12,3,X).

X = 12

12.2.                  Min number

Code:

min(X,Y,X):- X=<Y.

min(X,Y,Y):- X> Y.

Output:

min(12,3,X).

X = 3.