Haskell solution for http://habrahabr.ru/post/200190/

CityFlood

module Main where 

import qualified Data.Vector as V

printArray :: (Integral a, Show a) => V.Vector a -> IO ()
printArray x = mapM_ printLine $ reverse [1 .. maxElem]
    where
        printLine n = (putWithOffset $ show n) >> mapM_ (putFiller n) [0 .. (V.length x)-1] >> putChar '\n'
        putWithOffset s 
            | length s < numberOffset = putStr s >> mapM_ (\x -> putChar ' ') [1 .. (length s) - numberOffset]
            | otherwise = putStr s 
        putFiller n i 
            | x V.! i >= n = putChar '#'
            | otherwise = putChar ' '
        numberOffset = length $ show maxElem
        maxElem = V.maximum x

water :: Integral a => V.Vector a -> a
water vec = inwater 0 0 0 vec
    where inwater ml mr ac vec
            | V.length vec <= 1   = ac
            | leftMax >= rightMax = inwater leftMax rightMax (ac + rightMax - V.last vec) (V.take (V.length vec - 1) vec)
            | otherwise           = inwater leftMax rightMax (ac + leftMax  - V.head vec) (V.drop 1 vec)
            where  
                leftMax  = if V.head vec > ml then V.head vec else ml
                rightMax = if V.last vec > mr then V.last vec else mr


input = V.fromList [2,5,1,3,1,2,1,7,5,6]

main = do 
    printArray input
    putStrLn $ show $ water input

CityFlood_reduced

water :: Integral a => [a] -> a
water vec = inwater 0 0 0 vec
    where inwater ml mr ac vec
            | length vec <= 1   = ac
            | leftMax >= rightMax = inwater leftMax rightMax (ac + rightMax - last vec) (take (length vec - 1) vec)
            | otherwise           = inwater leftMax rightMax (ac + leftMax  - head vec) (drop 1 vec)
            where  
                leftMax   = if head vec > ml then head vec else ml
                rightMax  = if last vec > mr then last vec else mr

main = putStrLn $ show $ water [2,5,1,3,1,2,1,7,5,6]