praxis

commit d02914e2af82bc6003b212da07f48d5c3f18f60b
parent 2dca80dff754ec33b0b3476b693dad4dc8885a90
Author: Jared Tobin <jared@jtobin.ca>
Date:   Tue,  3 Jul 2018 10:12:24 +1200

Add Pearson hashing exercise.

Diffstat:
A
20180525_pearson/Hash.hs
 | 
53
+++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 53 insertions(+), 0 deletions(-)
diff --git a/20180525_pearson/Hash.hs b/20180525_pearson/Hash.hs
@@ -0,0 +1,53 @@
+{-# OPTIONS_GHC -Wall #-}
+{-# LANGUAGE ViewPatterns #-}
+
+import Data.Char as C
+import Data.List as L (foldl')
+import Data.Monoid ((<>))
+import qualified Data.Map.Strict as MS
+
+ptable :: MS.Map Int Int
+ptable = MS.fromList $
+  zip [0..255]
+    [ 1, 87, 49, 12, 176, 178, 102, 166, 121, 193, 6, 84, 249, 230, 44, 163
+    , 14, 197, 213, 181, 161, 85, 218, 80, 64, 239, 24, 226, 236, 142, 38, 200
+    , 110, 177, 104, 103, 141, 253, 255, 50, 77, 101, 81, 18, 45, 96, 31, 222
+    , 25, 107, 190, 70, 86, 237, 240, 34, 72, 242, 20, 214, 244, 227, 149, 235
+    , 97, 234, 57, 22, 60, 250, 82, 175, 208, 5, 127, 199, 111, 62, 135, 248
+    , 174, 169, 211, 58, 66, 154, 106, 195, 245, 171, 17, 187, 182, 179, 0, 243
+    , 132, 56, 148, 75, 128, 133, 158, 100, 130, 126, 91, 13, 153, 246, 216, 219
+    , 119, 68, 223, 78, 83, 88, 201, 99, 122, 11, 92, 32, 136, 114, 52, 10
+    , 138, 30, 48, 183, 156, 35, 61, 26, 143, 74, 251, 94, 129, 162, 63, 152
+    , 170, 7, 115, 167, 241, 206, 3, 150, 55, 59, 151, 220, 90, 53, 23, 131
+    , 125, 173, 15, 238, 79, 95, 89, 16, 105, 137, 225, 224, 217, 160, 37, 123
+    , 118, 73, 2, 157, 46, 116, 9, 145, 134, 228, 207, 212, 202, 215, 69, 229
+    , 27, 188, 67, 124, 168, 252, 42, 4, 29, 108, 21, 247, 19, 205, 39, 203
+    , 233, 40, 186, 147, 198, 192, 155, 33, 164, 191, 98, 204, 165, 180, 117, 76
+    , 140, 36, 210, 172, 41, 54, 159, 8, 185, 232, 113, 196, 231, 47, 146, 120
+    , 51, 65, 28, 144, 254, 221, 93, 189, 194, 139, 112, 43, 71, 109, 184, 209
+    ]
+
+hash8 :: String -> String
+hash8 (fmap C.ord -> bytes) = show (L.foldl' alg 0 bytes) where
+  alg acc byte =
+    let key = (acc + byte) `mod` 256
+    in  case MS.lookup key ptable of
+          Nothing  -> error "hash8: missing key"
+          Just val -> val
+
+hash16 :: String -> String
+hash16 input = hash0 <> hash1 where
+  hash0 = hash8 input
+  hash1 = hash8 modified
+
+  mbytes = case fmap C.ord input of
+    []    -> []
+    (h:t) -> (h + 1) `mod` 256 : t
+
+  modified = fmap C.chr mbytes
+
+main :: IO ()
+main = do
+  print (hash8 "Programming Praxis")
+  print (hash16 "Programming Praxis")
+