import Data.Char

longestNum [] = []
longestNum (x:xs) =
    let withCount = foldl (\((prev, cnt):acc) x ->
            if x==prev then (x,cnt+1):acc else (x,1):(prev,cnt):acc) [(x, 1)] xs
        digitsOnly = filter (isDigit . fst) withCount
        max = foldl1 (\(maxChar, maxCount) (candidateChar, candidateMax) ->
            if candidateMax > maxCount then (candidateChar, candidateMax) else (maxChar, maxCount)) digitsOnly
    in if digitsOnly == []
        then []
        else take (snd max) $ repeat (fst max)



reduceStr :: String -> String
reduceStr xs = let res = (reduceStrOnce xs)
                    in
                        if(xs == res)
                            then res
                            else reduceStr res

reduceStrOnce :: String -> String
reduceStrOnce [] = []
reduceStrOnce [x] = [x]
reduceStrOnce (x:y:xs) = if((((toUpper x) == y) || ((toLower x) == y)) && x /= y)
                        then reduceStrOnce(xs)
                        else [x] ++ reduceStrOnce(y:xs)





line :: (Double , Double ) -> (Double , Double ) -> (Double -> Double)
line (x1,y1) (x2,y2) = (\x -> y1 + (((x-x1)*(y2-y1)) /(x2-x1)))

liesOn :: (Double -> Double) ->((Double , Double) -> Bool)
liesOn f = (\(x1,y1) -> (if (f x1) == y1
                                then True
                                else False))


data BTree = NullT | Node (Float,Float) BTree BTree

orderedTree :: BTree -> Bool
orderedTree tree = compareTree (inorderTree tree)


inorderTree :: BTree ->[(Float,Float)]
inorderTree NullT =  []
inorderTree (Node (a,b) t1 t2) =  (inorderTree t1) ++ [(a,b)] ++ (inorderTree t2)

compareTree :: [(Float,Float)] -> Bool
compareTree [] = True
compareTree [x] = True
compareTree ((a,b) :(c,d):xs)
    | (c <= a) && (b <= d) = compareTree ((c,d):xs)
    | otherwise = False






verify actual expected =
    if actual == expected
        then "OK"
        else error ("Expected " ++ (show expected) ++ " actual " ++ (show actual))

main = do
    print "task 1"
    print $ verify (longestNum "") ""
    print $ verify (longestNum "1") "1"
    print $ verify (longestNum "a") ""
    print $ verify (longestNum "122") "22"
    print $ verify (longestNum "122000") "000"
    print $ verify (longestNum "11111ddddddd11111") "11111"
    print $ verify (longestNum "ab1d22b1b434442cd31d22e1eff") "444"
    print $ verify (longestNum "44ab1444111d22b1b4344442cd31ccccccd224e1eff44") "4444"
    print "task 2 reduceStr"
    -- print $ verify (reduceStr "") ""
    print $ verify (reduceStr "Aa") ""
    print $ verify (reduceStr "BaAb") ""
    print $ verify (reduceStr "aabbccddAABBCCDD") "aabbccddAABBCCDD"
    print $ verify (reduceStr "aCaAcb") "ab"
    print $ verify (reduceStr "dabAcCaCBAcCcaDD") "dabCBAcaDD"
    print $ verify (reduceStr "abcdDCBA") ""
    print "task 3 line"
    print $ verify (line (1, 1) (3, 2) 0) 0.5
    print $ verify (line (1, 1) (3, 2) 2) 1.5
    print $ verify (line (1, 1) (3, 2) 1) 1
    print $ verify (line (1, 1) (3, 2) 3) 2
    print $ verify (line (1, 1) (3, 2) (-1)) 0
    print "task 3 liesOn"
    print $ verify (liesOn (line (1, 1) (3, 2)) (0, 0.5)) True
    print $ verify (liesOn (line (1, 1) (3, 2)) (1, 1)) True
    print $ verify (liesOn (line (1, 1) (3, 2)) (3, 2)) True
    print $ verify (liesOn (line (1, 1) (3, 2)) (2, 1.5)) True
    print $ verify (liesOn (line (1, 1) (3, 2)) ((-1), 0)) True
    print $ verify (liesOn (line (1, 1) (3, 2)) (1, 0)) False
    print "task 4 orderedTree"
    print $ verify (orderedTree t11) False
    print $ verify (orderedTree t12) True
    print $ verify (orderedTree t13) False
    print $ verify (orderedTree t14) True
    print $ verify (orderedTree t1) True
    print $ verify (orderedTree t2) False
    -- print $ verify (orderedTree t15) False


t11 = Node (1.0, 3.0) (Node (1.0, 4.0) NullT NullT) NullT
t12 = Node (1.0, 3.0) (Node (2.0, 2.5) NullT NullT) NullT
t13 = Node (1.0, 3.0) NullT (Node (2.0, 3.5) NullT NullT)
t14 = Node (1.0, 3.0) NullT (Node (0.0, 3.5) NullT NullT)
t15 = Node (1.0, 10.0) (Node (2.0, 9.0) NullT (Node (1.0, 15.0) NullT NullT)) NullT

t1 = Node (3.0, 10.0) (Node (5.0, 8.0) (Node (6.0, 7.0) NullT NullT)
                                            (Node (4.0, 9.0) NullT NullT))
                           (Node (2.0, 12.0) NullT
                                             (Node (1.0, 15.0) NullT NullT))

t2 =  Node (3.0, 10.0) (Node (5.0, 8.0) (Node (6.0, 7.0) NullT NullT)
                                                (Node (7.0, 9.0) NullT NullT))
                                (Node (2.0, 12.0) NullT
                                                (Node (1.0, 15.0) NullT NullT))