Pascal's triangle/Puzzle: Difference between revisions
Content added Content deleted
m (Biggified header) |
(Added Haskell example) |
||
Line 1:
{{task}}{{puzzle}}
<pre>
[ 151]
Line 12 ⟶ 13:
'''Task:'''
*Find a solution of this puzzle.
=={{header|Haskell}}==
I assume the task is to solve any such puzzle, i.e. given some data
<pre>
puzzle = [["151"],["",""],["40","",""],["","","",""],["X","11","Y","4","Z"]]
</pre>
one should calculate all possible values that fit. That just means solving a linear system of equations. We use the first three variables as placeholders for ''X'', ''Y'' and ''Z''. Then we can produce the matrix of equations:
<pre>
triangle n = n * (n+1) `div` 2
coeff xys x = maybe 0 id $ lookup x xys
row n cs = [coeff cs k | k <- [1..n]]
eqXYZ n = [(0, 1:(-1):1:replicate n 0)]
eqPyramid n h = do
a <- [1..h-1]
x <- [triangle (a-1) + 1 .. triangle a]
let y = x+a
return $ (0, 0:0:0:row n [(x,-1),(y,1),(y+1,1)])
eqConst n fields = do
(k,s) <- zip [1..] fields
guard $ not $ null s
return $ case s of
"X" - (0, 1:0:0:row n [(k,-1)])
"Y" - (0, 0:1:0:row n [(k,-1)])
"Z" - (0, 0:0:1:row n [(k,-1)])
_ - (fromInteger $ read s, 0:0:0:row n [(k,1)])
equations :: [[String]] - ([Rational], [[Rational]])
equations puzzle = unzip eqs where
fields = concat puzzle
eqs = eqXYZ n ++ eqPyramid n h ++ eqConst n fields
h = length puzzle
n = length fields
</pre>
To solve the system, any linear algebra library will do (e.g [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix-0.2.0.0 hmatrix]). For this example, we assume there are functions ''decompose'' for LR-decomposition, ''kernel'' to solve the homogenous system and ''solve'' to find a special solution for an imhomogenous system. Then
<pre>
normalize :: [Rational] - [Integer]
normalize xs = [numerator (x * v) | x <- xs] where
v = fromInteger $ foldr1 lcm $ map denominator $ xs
run puzzle = map (normalize . drop 3) $ answer where
(a, m) = equations puzzle
lr = decompose 0 m
answer = case solve 0 lr a of
Nothing - []
Just x - x : kernel lr
</pre>
will output one special solution and modifications that lead to more solutions, as in
<pre>
*Main run puzzle
[[151,81,70,40,41,29,16,24,17,12,5,11,13,4,8]]
*Main run [[""],["2",""],["X","Y","Z"]]
[[3,2,1,1,1,0],[3,0,3,-1,1,2]]
</pre>
so for the second puzzle, not only X=1 Y=1 Z=0 is a solution, but also X=1-1=0, Y=1+1=2 Z=0+2=2 etc.
Note that the program doesn't attempt to verify that the puzzle is in correct form.
=={{header|Oz}}==
| |||