Koitaro

-module(problem50).
-include("euler.hrl").

answer() ->
    F = fun(L) -> longest(lists:reverse(L)) end,
    element(2, lists:max(lists:map(F, tails(primes())))).

longest([]) -> {0,0};
longest([H|T]) ->
    X = lists:sum([H|T]),

Koitaro

-module(problem40).
-include("euler.hrl").

answer() -> prod([digit(N) || N <- [1,10,100,1000,10000,100000,1000000]]).

digit(N) -> digit(N,0,0).

digit(N,0,0) when N < 10 -> N;
digit(N,D,T) ->
    X = 9 * trunc(math:pow(10,D)),

Koitaro

-module(problem30).
-include("euler.hrl").

answer() -> sum(tree([]), max_digits(1)).

tree([])    -> {[],    [fun() -> tree([X]) end || X <- lists:seq(0,9)]};
tree([H|T]) -> {[H|T], [fun() -> tree([X,H|T]) end || X <- lists:seq(0,H)]}.

sum({L,_}, Max) when length(L) =:= Max -> sum_fifth(L);
sum({L,Fs},Max) -> sum_fifth(L) + lists:sum([sum(F(),Max) || F <- Fs]).

Koitaro

-module(max_heap).
-export([new/0, push/2, pop/1]).

new() -> empty.

push(X,H) -> merge({X,[]}, H).

pop({X,L}) -> {X, lists:foldl(fun merge/2, empty, pair(L))}.

merge(X,empty)     -> X;

Koitaro

-module(problem20).
-include("euler.hrl").

answer() -> lists:sum(i2d(fact(100))).

fact(0) -> 1;
fact(N) -> N * fact(N-1).

Koitaro

-module(problem10).
-include("euler.hrl").

answer() ->
    S = primes(2000000),
    try
        ets:foldl(fun({X},Y) -> X+Y end, 0, S)
    after
        ets:delete(S)
    end.

Koitaro

-compile(export_all).

-define(even(X), X rem 2 =:= 0).
-define(odd(X),  X rem 2 =/= 0).

main() -> timer:tc(?MODULE, answer, []).

pow(_,0)                      -> 1;
pow(X,Y) when Y > 0, ?even(Y) -> Z = pow(X, Y div 2), Z*Z;
pow(X,Y) when Y > 0           -> Z = pow(X, Y div 2), X*Z*Z.

Koitaro

:- use_module(library(chr)).
:- chr_option(optimize, full).
:- chr_type list(T) ---> []; [T|list(T)].
:- chr_constraint
	digit(+int),
	num(+int,+list(int)),
	answer(+int),
	problem206.

problem206 <=> digit(9), num(1,[0]).

Koitaro

:- use_module(library(chr)).
:- chr_option(optimize, full).
:- chr_constraint triangle(+int,+int,+int), answer(+int), problem139.

problem139 <=> triangle(3,4,5).

next_triangle(A,B,C) :-
	X is -A-2*B+2*C, Y is -2*A-B+2*C, Z is -2*A-2*B+3*C,
	triangle(X,Y,Z).

Koitaro

:- use_module(library(chr)).
:- chr_option(optimize, full).
:- chr_type list(T) ---> []; [T|list(T)].
:- chr_type heap(T) ---> int-list(heap(T)).
:- chr_constraint
	heap(+heap(int)),
	next(+int,+int,+int),
	way(+int),
	cube(+int,+int,+int),
	diff(+int),