Problem:
0-1 Knapsack Problem

You have N items that you want to put them into a knapsack. Item i has value vi and weight wi.

You want to find a subset of items to put such that:

The total value of the items is as large as possible.

The items have combined weight at most W, that is capacity of the knapsack.

Find the maximum total value of items in the knapsack.

Input

N W
v1 w1
v2 w2
:
vN wN

The first line consists of the integers N and W. In the following lines, the value and weight of the i-th item are given.

Output

Print the maximum total values of the items in a line.

Constraints

1 ≤ N ≤ 100

1 ≤ vi ≤ 1000

1 ≤ wi ≤ 1000

1 ≤ W ≤ 10000

Sample Input 1

4 5
4 2
5 2
2 1
8 3

Sample Output 1

13

Sample Input 2

2 20
5 9
4 10

Sample Output 2

9

Solution in Haskell (judge verdict: Accepted)

import Control.Monad
import Control.Applicative
import Data.List
import Data.Array.IO

type Value = Int
type Weight = Int
type Item = (Weight, Value)
type ItemList = [Item]
type Capacity = Int

main :: IO ()
main = do
  input <- getContents
  let nums = map ((\x -> (last x, head x)) . map (read :: String -> Int) . words) . lines $ input
      capacity = fst . head $ nums
      items = tail nums

  memo <- newArray ((0, 0), (capacity, length items)) (0 - 1) :: IO (IOUArray (Int, Int) Int)
  dp (capacity, items) memo
  putStrLn . show . last =<< getElems memo

memoize :: ((Capacity, ItemList) -> IOUArray (Int, Int) Int -> IO (IOUArray (Int, Int) Int)) -> (Capacity, ItemList) -> IOUArray (Int, Int) Int -> IO Int
memoize f (c, i) t = do
  v <- readArray t (c, length i)
  if v < 0
    then do
      f (c, i) t
      return =<< readArray t (c, length i)
    else return v

dp :: (Capacity, ItemList) -> IOUArray (Int, Int) Int -> IO (IOUArray (Int, Int) Int)
dp (c, []) t = do
  writeArray t (c, 0) 0
  return t
dp (c, as@(i:is)) t
{-
  | c <= 0    = do
    writeArray t (0, length as) 0
    dp (c, is) t
    return t
    -}
  | c < fst i = do
    v <- memoize dp (c, is) t
    writeArray t (c, length as) v
    return t
  | otherwise = do
    x <- memoize dp (c, is) t
    y <- memoize dp (c - fst i, is) t
    writeArray t (c, length as) (max x $ y + snd i)
    return t