/*

  Euler problem 42 in SICStus Prolog

  """
  The nth term of the sequence of triangle numbers is given by, 
      tn = 1/2*n*(n+1); 
  so the first ten triangle numbers are:

  1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

  By converting each letter in a word to a number corresponding to its 
  alphabetical position and adding these values we form a word value. For example, 
  the word value for SKY is 19 + 11 + 25 = 55 = t10. If the word value 
  is a triangle number then we shall call the word a triangle word.

  Using words.txt (right click and 'Save Link/Target As...'), a 16K text file 
  containing nearly two-thousand common English words, how many 
  are triangle words?
  """

  Model created by Hakan Kjellerstrand, hakank@gmail.com
  See also my SICStus Prolog page: http://www.hakank.org/sicstus_prolog/

*/

:- ensure_loaded(hakank_utils).

:- set_prolog_flag(double_quotes,chars).

go :- 
        L = [
             euler42a
            ],
        run_problems(L).
             
%%
%% 0.011s
%%
euler42a :-
    read_file('euler42_names.txt',Str1),
    Str1 = [Str|_],
    delete(Str,34,Str2), % '"'
    split_string(Str2,44,Lines), % ','
    numlist(1,100,Is),
    maplist(triangle_number,Is,Ts),
    findall(Ss,
            (member(S,Lines),
             upper_string_to_digit_list(S,D),
             sum_list(D,Ss),
             memberchk(Ss,Ts)
            ),
            L
           ),
    length(L,Len),
    writeln(Len).

triangle_number(N,T) :-
    T is (N*(N+1)) div 2.

upper_string_to_digit_list(N,L) :-
    maplist(to_upper_alpha,N,L).

to_upper_alpha(N,Alpha) :-
    Alpha is N - 64.