rewrite and write 2~8

Prime.hs

@@ -0,0 +1,7 @@
+
+module Prime where
+
+primes = primes_inner [] [2 ..]
+    where
+    primes_inner ps (x:xs) = x:(primes_inner (x:ps) [n | n<-xs, n `mod` x /= 0])
+

euler002.hs

@@ -1,12 +1,7 @@
 
-fib_sum n = fib_sum_inner [1,0]
+fibonaccis = fib_inner 0 1
 	where
-	fib_sum_inner s@(x1:x2:xs)
-		| x > n = 0
-		| otherwise = even_value x + fib_sum_inner (x:s)
-		where
-			x = x1 + x2
-			even_value n = if even n then n else 0
+	fib_inner a b = a:(fib_inner b (a+b))
 
 main = do
-	print $ fib_sum 4000000
+	print $ sum (takeWhile (<= 4000000) ([n|n<-fibonaccis,even n]))

euler003.hs

@@ -1,7 +1,5 @@
 
-primes = primes_inner [] [2 ..]
-	where
-	primes_inner ps (x:xs) = x:(primes_inner (x:ps) [n | n<-xs, n `mod` x /= 0])
+import Prime
 
 factors n
 	| n < 2 = [n]

euler004.hs

@@ -0,0 +1,16 @@
+
+is_palindrome n = n == reverse_num n 0
+	where
+	reverse_num 0 tgt = tgt
+	reverse_num src tgt = reverse_num (src `div` 10) (tgt * 10 + (src `mod` 10))
+
+max_palindrome n = mp_inner n n 0
+	where
+	mp_inner a b max
+		| a * 2 < n = max
+		| a * b < max = mp_inner (a-1) (a-1) max
+		| is_palindrome (a*b) = mp_inner (a-1) (a-1) (a*b)
+		| otherwise = mp_inner a (b-1) max
+
+main = do
+	print $ max_palindrome 999

euler005.bruteforce.hs

@@ -0,0 +1,10 @@
+
+lcm' ns = lcm_inner ns 1
+	where
+	lcm_inner [] r = r
+	lcm_inner ns r
+		| foldl (&&) True (map ((0 ==).(r `mod`)) ns) = r
+		| otherwise = lcm_inner ns (r+1)
+
+main = do
+	print $ lcm' [1 .. 20]

euler005.hs

@@ -0,0 +1,9 @@
+
+lcm' [] = 0
+lcm' ns = lcm_inner ns 1
+	where
+	lcm_inner [] r = r
+	lcm_inner (n:ns) r = lcm_inner ns (r * (n `div` (gcd n r)))
+
+main = do
+	print $ lcm' [1 .. 20]

euler006.hs

@@ -0,0 +1,5 @@
+
+square_diff n = (sum [1..n]) ^2 - (sum (map (^2) [1..n]))
+
+main = do
+	print $ square_diff 100

euler007.hs

@@ -0,0 +1,5 @@
+
+import Prime
+
+main = do
+	print $ primes !! (10001 -1)

euler008.hs

@@ -0,0 +1,37 @@
+
+import Char
+
+numstring = 
+	"73167176531330624919225119674426574742355349194934" ++ 
+	"96983520312774506326239578318016984801869478851843" ++
+	"85861560789112949495459501737958331952853208805511" ++
+	"12540698747158523863050715693290963295227443043557" ++
+	"66896648950445244523161731856403098711121722383113" ++
+	"62229893423380308135336276614282806444486645238749" ++
+	"30358907296290491560440772390713810515859307960866" ++
+	"70172427121883998797908792274921901699720888093776" ++
+	"65727333001053367881220235421809751254540594752243" ++
+	"52584907711670556013604839586446706324415722155397" ++
+	"53697817977846174064955149290862569321978468622482" ++
+	"83972241375657056057490261407972968652414535100474" ++
+	"82166370484403199890008895243450658541227588666881" ++
+	"16427171479924442928230863465674813919123162824586" ++ 
+	"17866458359124566529476545682848912883142607690042" ++
+	"24219022671055626321111109370544217506941658960408" ++ 
+	"07198403850962455444362981230987879927244284909188" ++ 
+	"84580156166097919133875499200524063689912560717606" ++
+	"05886116467109405077541002256983155200055935729725" ++
+	"71636269561882670428252483600823257530420752963450"
+
+max_mult cs = max_mult_inner cs 0
+	where
+	max_mult_inner s@(_:cs) old_max
+		| length s < 5 = old_max
+		| otherwise = max_mult_inner cs new_max
+		where
+		cval c = (ord c) - (ord '0')
+		mult = foldl (*) 1 (map cval (take 5 s))
+		new_max = if mult > old_max then mult else old_max
+
+main = do
+	print $ max_mult numstring