Add code to find self describing numbers.

See: https://www.youtube.com/watch?v=1GKfEDvhWdY
bxt · Jan 12, 2016 · 2ea8a57 · 2ea8a57
1 parent fcb346c
commit 2ea8a57
Showing 1 changed file with 11 additions and 0 deletions.
diff --git a/unilectures.hs/selfDescribing.hs b/unilectures.hs/selfDescribing.hs
@@ -0,0 +1,11 @@
+import Data.List
+import Control.Monad (ap)
+
+isSelfDescribing n = sn == desc sn
+  where desc = concatMap (show . pred . length) . group . sort . (['0'..to] ++)
+        to   = head $ show $ pred $ length sn
+        sn   = show n
+
+selfDescribing = filter isSelfDescribing [1 ..]
+
+main = print selfDescribing