module Util where

import Data.List (transpose)
import System.Random

-- | Square.
square :: Int -> Int
square x = x * x

-- | Make pair.
pair :: a -> b -> (a, b)
pair a b = (a, b)

-- | Replace i-th element of list to v.
replace :: [a] -> Int -> a -> [a]
replace ls i v = take i ls ++ [v] ++ drop  (i + 1) ls

-- | Remove i-th element of list.
remove :: Int -> [a] -> [a]
remove i = (\(xs, ys) -> xs ++ tail ys) . splitAt i

-- | Rotate 2-D list clock-wise.
rotate :: Int -> [[a]] -> [[a]]
rotate 0     xss = xss
rotate (n + 1) xss = rotate n $ transpose $ reverse xss

-- | Map 2-D list with index.
idxmap2 :: ((Int, Int) -> a -> b) -> [[a]] -> [[b]]
idxmap2 f = zipWith (\iy -> zipWith (\ix c -> f (ix,iy) c) [0..]) [0..]

-- |Random integer number: 0..n-1
randN :: Int -> IO Int
randN n = getStdRandom (randomR (0, n - 1))