List comprehensions: Difference between revisions
Content added Content deleted
No edit summary |
m (fixed link) |
||
Line 1: | Line 1: | ||
{{task}} |
{{task}} |
||
A [ |
A [http://en.wikipedia.org/wiki/List_comprehension list comprehension] is a special syntax in some programming languages to describe lists. It is similar to the way mathematicians describe sets, with a ''set comprehension'', hence the name. |
||
Write a list comprehension that builds the list of all pythagorean triples with elements between 1 and n. If the language has multiple ways for expressing such a construct (for example, direct list comprehensions and generators), write one example for each. |
Write a list comprehension that builds the list of all pythagorean triples with elements between 1 and n. If the language has multiple ways for expressing such a construct (for example, direct list comprehensions and generators), write one example for each. |
Revision as of 18:11, 23 May 2008
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
You are encouraged to solve this task according to the task description, using any language you may know.
A list comprehension is a special syntax in some programming languages to describe lists. It is similar to the way mathematicians describe sets, with a set comprehension, hence the name.
Write a list comprehension that builds the list of all pythagorean triples with elements between 1 and n. If the language has multiple ways for expressing such a construct (for example, direct list comprehensions and generators), write one example for each.
E
pragma.enable("accumulator") # considered experimental accum [] for x in 1..n { for y in x..n { for z in y..n { if (x**2 + y**2 <=> z**2) { _.with([x,y,z]) } } } }
Erlang
pythag(N) -> [ {A,B,C} || A <- lists:seq(1,N), B <- lists:seq(1,N), C <- lists:seq(1,N), A+B+C =< N, A*A+B*B == C*C ].
Haskell
pyth n = [(x,y,z) | x <- [1..n], y <- [x..n], z <- [y..n], x^2 + y^2 == z^2]
Since lists are Monads, one can alternatively also use the do-notation (which is practical if the comprehension is large):
import Control.Monad pyth n = do x <- [1..n] y <- [x..n] z <- [y..n] guard $ x^2 + y^2 == z^2 return (x,y,z)
Pop11
lvars n = 10, i, j, k; [% for i from 1 to n do for j from 1 to n do for k from 1 to n do if i*i + j*j = k*k then [^i ^j ^k]; endif; endfor; endfor; endfor %] =>
Python
[(x,y,z) for x in xrange(1,21) for y in xrange(x,21) for z in xrange(y,21) if x**2 + y**2 == z**2]
TODO: Alternative with generators