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+#!/usr/bin/env runghc
+
+import Data.Char (isDigit)
+import Data.List ((\\), inits)
+import Data.Tree (Tree, drawTree, unfoldTree)
+import System.Environment (getArgs)
+
+sumMinNrs :: [String] -> [String]
+sumMinNrs xs = map (\x -> if (all isDigit x) then show (sm - ((read::String->Int)) x) else x) xs where
+  sm = sum $ map (read::String->Int) $ filter (all isDigit) xs
+
+split2trees :: [String] -> ([String],[String])
+split2trees xs = (lhalf, xs \\ lhalf) where
+  lhalf = head $ dropWhile (\ys -> 2*(length $ filter (\s -> s==".") ys) <= length ys ) $ inits xs
+
+nodeIter :: [String] -> (String, [[String]])
+nodeIter xs = if (head xs == ".") then ("",[]) else (head xs, [lchild,rchild]) where
+  (lchild,rchild) = split2trees $ tail xs
+
+mkTree :: [String] -> Tree String
+mkTree  = unfoldTree nodeIter
+  
+main = do
+  outTreeList <- getArgs >>= return . sumMinNrs . (\x -> if (not $ null x) then x else ["1", "2", "4", ".", "7", ".", ".", ".", "3", "5", ".", ".", "6", ".", "."])  
+  putStrLn $ drawTree $ mkTree outTreeList
+{--
+run <script> <tree in preorder form with '.' for empty nodes, entered as space-separated values>
+
+ref: https://stackoverflow.com/a/2676849/11064961
+
+e.g. 1 2 4 . 7 . . . 3 5 . . 6 . . represents the tree
+
+        1
+       / \
+      2   3
+     /   / \
+    4   5   6
+     \
+      7
+
+given as an example in the problem formulation at https://perlweeklychallenge.org/blog/perl-weekly-challenge-113/#TASK2
+--}