Add functions for comparing trees.

One approach to crossover for trees is to swap subtrees at a shared
point in the two trees. These functions will help with that.

Author: msgodf

package.yaml

@@ -23,6 +23,7 @@ dependencies:
 - base >= 4.11 && < 5
 - random
 - QuickCheck
+- containers
 
 library:
   source-dirs: src
@@ -38,6 +39,7 @@ executables:
     dependencies:
     - hs
     - random
+    - containers
 
 tests:
   hs-test:

src/Tree.hs

@@ -64,3 +64,11 @@ maxDepth :: Int -> Tree -> Int
 maxDepth d (Branch o a b) = if m > n then m else n where m = maxDepth (d + 1) a
                                                          n = maxDepth (d + 1) b
 maxDepth d (Leaf a) = d
+
+labelTree :: Tree -> Int -> Set Int -> Set Int
+labelTree (Leaf a) n xs = (singleton n) `union` xs
+labelTree (Branch o a b) n xs = (singleton n) `union` (labelTree a (2*n + 1) xs) `union` (labelTree b (2*n + 2) xs)
+
+intersectionOfTreeLabels :: Tree -> Tree -> Set Int
+intersectionOfTreeLabels t1 t2 = (labelTree t2 0 empty) `intersection` (labelTree t1 0 empty)
+