fermat factorization

fermat-factorization.hs

@@ -0,0 +1,35 @@
+import Text.Read (readMaybe)
+import System.Exit (exitSuccess)
+
+
+main :: IO ()
+main = do
+    n <- askNumber
+    let (d, root) = findIntegerSqrt n
+        q = (root - d)
+        p = (root + d)
+    putStrLn ("n = " ++ show n)
+    putStrLn ("Found d = " ++ show d ++ ", sqrt(n + d^2) = " ++ show root)
+    putStrLn ("q = " ++ show q ++ ", p = " ++ show p)
+
+
+askNumber :: IO Int
+askNumber = do
+    putStrLn "Enter an integer:"
+    input <- getLine
+    case readMaybe input :: Maybe Int of
+        Just n  -> return n
+        Nothing -> do
+            putStrLn "Not a valid integer!"
+            exitSuccess
+
+-- Find the smallest integer d >= 0 such that sqrt(n + d^2) is an integer
+findIntegerSqrt :: Int -> (Int, Int)
+findIntegerSqrt n = go 0
+  where
+    go d =
+        let val  = n + d*d
+            root = floor (sqrt (fromIntegral val))
+        in if root * root == val
+           then (d, root)
+           else go (d + 1)