{-# LANGUAGE Rank2Types #-} ----------------------------------------------------------------------------- -- | -- Module : Data.Permute -- Copyright : Copyright (c) , Patrick Perry <patperry@stanford.edu> -- License : BSD3 -- Maintainer : Patrick Perry <patperry@stanford.edu> -- Stability : experimental -- -- Immutable permutations. module Data.Permute ( -- * Permutations Permute, -- * Creating permutations permute, listPermute, swapsPermute, -- * Accessing permutation elements at, unsafeAt, -- * Permutation properties size, elems, -- * Permutation functions inverse, next, prev, -- * Applying permutations swaps, invSwaps, -- * Sorting sort, sortBy, order, orderBy, rank, rankBy, ) where import Control.Monad import Control.Monad.ST import Data.Permute.Base import Data.Permute.ST -- | Construct an identity permutation of the given size. permute :: Int -> Permute permute n = runST $ unsafeFreeze =<< newPermute n -- | Construct a permutation from a list of elements. -- @listPermute n is@ creates a permutation of size @n@ with -- the @i@th element equal to @is !! i@. For the permutation to be valid, -- the list @is@ must have length @n@ and contain the indices @0..(n-1)@ -- exactly once each. listPermute :: Int -> [Int] -> Permute listPermute n is = runST $ unsafeFreeze =<< newListPermute n is -- | Construct a permutation from a list of swaps. -- @swapsPermute n ss@ creats a permutation of size @n@ given by a -- sequence of swaps. -- If @ss@ is @[(i0,j0), (i1,j1), ..., (ik,jk)]@, the -- sequence of swaps is -- @i0 \<-> j0@, then -- @i1 \<-> j1@, and so on until -- @ik \<-> jk@. swapsPermute :: Int -> [(Int,Int)] -> Permute swapsPermute n ss = runST $ unsafeFreeze =<< newSwapsPermute n ss -- | @at p i@ gets the value of the @i@th element of the permutation -- @p@. The index @i@ must be in the range @0..(n-1)@, where @n@ is the -- size of the permutation. at :: Permute -> Int -> Int at p i | i >= 0 && i < size p = unsafeAt p i | otherwise = error "Invalid index" {-# INLINE at #-} -- | Get the inverse of a permutation inverse :: Permute -> Permute inverse p = runST $ unsafeFreeze =<< getInverse =<< unsafeThaw p -- | Return the next permutation in lexicographic order, or @Nothing@ if -- there are no further permutations. Starting with the identity permutation -- and repeatedly calling this function will iterate through all permutations -- of a given order. next :: Permute -> Maybe Permute next = nextPrevHelp setNext -- | Return the previous permutation in lexicographic order, or @Nothing@ -- if no such permutation exists. prev :: Permute -> Maybe Permute prev = nextPrevHelp setPrev nextPrevHelp :: (forall s. STPermute s -> ST s Bool) -> Permute -> Maybe Permute nextPrevHelp set p = runST $ do p' <- thaw p set p' >>= \valid -> if valid then liftM Just $ unsafeFreeze p' else return Nothing -- | Get a list of swaps equivalent to the permutation. A result of -- @[ (i0,j0), (i1,j1), ..., (ik,jk) ]@ means swap @i0 \<-> j0@, -- then @i1 \<-> j1@, and so on until @ik \<-> jk@. swaps :: Permute -> [(Int,Int)] swaps p = runST $ getSwaps =<< unsafeThaw p -- | Get a list of swaps equivalent to the inverse of permutation. invSwaps :: Permute -> [(Int,Int)] invSwaps p = runST $ getInvSwaps =<< unsafeThaw p -- | @sort n xs@ sorts the first @n@ elements of @xs@ and returns a -- permutation which transforms @xs@ into sorted order. The results are -- undefined if @n@ is greater than the length of @xs@. This is a special -- case of 'sortBy'. sort :: (Ord a) => Int -> [a] -> ([a], Permute) sort n xs = runST $ do (xs',mp) <- getSort n xs p <- unsafeFreeze mp return (xs',p) sortBy :: (a -> a -> Ordering) -> Int -> [a] -> ([a], Permute) sortBy cmp n xs = runST $ do (xs',mp) <- getSortBy cmp n xs p <- unsafeFreeze mp return (xs',p) -- | @order n xs@ returns a permutation which rearranges the first @n@ -- elements of @xs@ into ascending order. The results are undefined if @n@ is -- greater than the length of @xs@. This is a special case of 'orderBy'. order :: (Ord a) => Int -> [a] -> Permute order n xs = runST $ unsafeFreeze =<< getOrder n xs orderBy :: (a -> a -> Ordering) -> Int -> [a] -> Permute orderBy cmp n xs = runST $ unsafeFreeze =<< getOrderBy cmp n xs -- | @rank n xs@ eturns a permutation, the inverse of which rearranges the -- first @n@ elements of @xs@ into ascending order. The returned permutation, -- @p@, has the property that @p[i]@ is the rank of the @i@th element of @xs@. -- The results are undefined if @n@ is greater than the length of @xs@. -- This is a special case of 'rankBy'. rank :: (Ord a) => Int -> [a] -> Permute rank n xs = runST $ unsafeFreeze =<< getRank n xs rankBy :: (a -> a -> Ordering) -> Int -> [a] -> Permute rankBy cmp n xs = runST $ unsafeFreeze =<< getRankBy cmp n xs