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Haskell: added DFS Stack to Tree Traversal #395

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Oct 3, 2018
Merged

Haskell: added DFS Stack to Tree Traversal #395

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a86d698
Added DFS Stack
jiegillet Sep 29, 2018
0165d37
Fixed import lines after reformatting code
jiegillet Sep 29, 2018
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49 changes: 29 additions & 20 deletions contents/tree_traversal/code/haskell/TreeTraversal.hs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
data Tree a = Node { node :: a
, forest :: [Tree a]
} deriving (Show)
data Tree a = Node
{ node :: a
, forest :: [Tree a]
} deriving (Show)

dfs :: Tree a -> [a]
dfs (Node x ts) = x : concatMap dfs ts
Expand All @@ -9,15 +10,22 @@ dfsPostOrder :: Tree a -> [a]
dfsPostOrder (Node x ts) = concatMap dfsPostOrder ts ++ [x]

dfsInOrder :: Tree a -> [a] -- For binary trees only
dfsInOrder (Node x []) = [x]
dfsInOrder (Node x [l]) = dfsInOrder l ++ [x] -- Single branch assumed to be left
dfsInOrder (Node x []) = [x]
dfsInOrder (Node x [l]) = dfsInOrder l ++ [x] -- Single branch assumed to be left
dfsInOrder (Node x [l, r]) = dfsInOrder l ++ [x] ++ dfsInOrder r
dfsInOrder _ = error "Not a binary tree"
dfsInOrder _ = error "Not a binary tree"

dfsStack :: Tree a -> [a]
dfsStack t = go [t]
where
go [] = []
go ((Node x ts):stack) = x : go (ts ++ stack)

bfs :: Tree a -> [a]
bfs (Node x ts) = x : go ts
where go [] = []
go ts = map node ts ++ go (concatMap forest ts)
where
go [] = []
go ts = map node ts ++ go (concatMap forest ts)

toBin :: Tree a -> Tree a
toBin (Node x ts) = Node x (map toBin $ take 2 ts)
Expand All @@ -26,18 +34,19 @@ main = do
print $ dfs testTree
print $ dfsPostOrder testTree
print $ dfsInOrder $ toBin testTree
print $ dfsStack testTree
print $ bfs testTree

testTree :: Tree Int
testTree = Node 1 [ Node 2 [ Node 3 []
, Node 4 [ Node 5 []]
]
, Node 6 [ Node 7 []
, Node 8 [ Node 9 [ Node 10 [ Node 11 []]
, Node 12 []
]
]
, Node 13 [ Node 14 []]
]
, Node 15 []
]
testTree =
Node
1
[ Node 2 [Node 3 [], Node 4 [Node 5 []]]
, Node
6
[ Node 7 []
, Node 8 [Node 9 [Node 10 [Node 11 []], Node 12 []]]
, Node 13 [Node 14 []]
]
, Node 15 []
]
13 changes: 6 additions & 7 deletions contents/tree_traversal/tree_traversal.md
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Expand Up @@ -25,7 +25,7 @@ This has not been implemented in your chosen language, so here is the Julia code
{% sample lang="rs"%}
[import:4-7, lang:"rust"](code/rust/tree.rs)
{% sample lang="hs"%}
[import:1-3, lang:"haskell"](code/haskell/TreeTraversal.hs)
[import:1-4, lang:"haskell"](code/haskell/TreeTraversal.hs)
{% sample lang="swift"%}
[import:1-9, lang:"swift"](code/swift/tree.swift)
{% sample lang="php"%}
Expand Down Expand Up @@ -59,7 +59,7 @@ Because of this, the most straightforward way to traverse the tree might be recu
{% sample lang="rs"%}
[import:9-15 lang:"rust"](code/rust/tree.rs)
{% sample lang="hs"%}
[import:5-6, lang:"haskell"](code/haskell/TreeTraversal.hs)
[import:6-7, lang:"haskell"](code/haskell/TreeTraversal.hs)
{% sample lang="swift"%}
[import:24-30, lang:"swift"](code/swift/tree.swift)
{% sample lang="php"%}
Expand Down Expand Up @@ -101,7 +101,7 @@ Now, in this case the first element searched through is still the root of the tr
{% sample lang="rs"%}
[import:17-23, lang:"rust"](code/rust/tree.rs)
{% sample lang="hs"%}
[import:8-9, lang:"haskell"](code/haskell/TreeTraversal.hs)
[import:9-10, lang:"haskell"](code/haskell/TreeTraversal.hs)
{% sample lang="swift"%}
[import:32-38, lang:"swift"](code/swift/tree.swift)
{% sample lang="php"%}
Expand Down Expand Up @@ -138,7 +138,7 @@ In this case, the first node visited is at the bottom of the tree and moves up t
{% sample lang="rs"%}
[import:25-38, lang:"rust"](code/rust/tree.rs)
{% sample lang="hs"%}
[import:11-15, lang:"haskell"](code/haskell/TreeTraversal.hs)
[import:12-16, lang:"haskell"](code/haskell/TreeTraversal.hs)
{% sample lang="swift"%}
[import:40-53, lang:"swift"](code/swift/tree.swift)
{% sample lang="php"%}
Expand Down Expand Up @@ -185,8 +185,7 @@ In code, it looks like this:
{% sample lang="rs"%}
[import:40-47, lang:"rust"](code/rust/tree.rs)
{% sample lang="hs"%}
This has not been implemented in your chosen language, so here is the Julia code
[import:45-56, lang:"julia"](code/julia/Tree.jl)
[import:18-22, lang:"haskell"](code/haskell/TreeTraversal.hs)
{% sample lang="swift"%}
[import:55-67, lang:"swift"](code/swift/tree.swift)
{% sample lang="php"%}
Expand Down Expand Up @@ -225,7 +224,7 @@ And this is exactly what Breadth-First Search (BFS) does! On top of that, it can
{% sample lang="rs"%}
[import:49-57, lang:"rust"](code/rust/tree.rs)
{% sample lang="hs"%}
[import:17-20, lang:"haskell"](code/haskell/TreeTraversal.hs)
[import:24-28, lang:"haskell"](code/haskell/TreeTraversal.hs)
{% sample lang="swift"%}
[import:69-81, lang:"swift"](code/swift/tree.swift)
{% sample lang="php"%}
Expand Down