Hi. I tried to solve one of the google code jam's problems using haskel http://code.google.com/codejam/contest/dashboard?c=90101#s=p2: w :: Eq a => [a] -> [a] -> Int w text str = w' (reverse text) (reverse str) w' :: Eq a => [a] -> [a] -> Int -- Init w' _ [] = 0 w' [] _ = 0 -- For one symbol string w' text [a] = if head text == a then w' (tail text) [a] +1 else w' (tail text) [a] -- General case w' text str = if head str == head text then w' (tail text) (tail str) + w' (tail text) str else w' (tail text) str and it worked great on small inputs, not on large: w "viwiwhiuwwwgxzseebneesgzxiekzeeyivrbbhzrlllccxczyurxfhhccghkzvxusfbcucyvncpzpvfvccxcvbqnqogobzoiorxrbikyzzbobpmmmmpmvrzyivpfmmuzxixhqpeebyekkxffeyexeiukuebgbrukzefeu rkxy z h x vkq fsyp iy tfyzbptygtsrkhbytvruztzbttnoxuquokipyyqoik ib xu gxchcnccuccyfcccccsczccskifcprgovryxuxoozqoozsvudyfkdpkkxyhdvfsrnvpnpzvrhqhbduidkdpdysinyxnuxnxipddevqhgeufxeepyyezbekyviieeeryiexynevbzfeezryizvepynefffy y v zuzrbpzn sz y vzirkxjniuqvjjbjgubnjkujhjpiyanaabrqagzqqvspqpkvqyuhrgupbaiaasxybiygmmfimyvykkmrzum" "welcome to code jam" Can you please advice how to optimize this solution? Thanks. Regards, Ivan Vovnenko