gistfile1.hs

import Data.Vector.Primitive.Mutable
import Control.Monad
import Prelude hiding (read)

newUF :: Int -> IO (IOVector Int)
newUF n = do
  v <- new n
  forM_ [0..n-1] $ \i -> write v i i
  return v

find a v = do
  b <- read v a
  if a==b
    then return a
    else do
    c <- find b v
    write v a c
    return c

unite a b v = do
  x <- find a v
  y <- find b v
  write v x y

main :: IO ()
main = do
  uf <- newUF 10
  unite 1 2 uf
  unite 2 3 uf
  print =<< find 1 uf
  print =<< find 2 uf
  print =<< find 3 uf
  print =<< find 4 uf