Adding Tree Traversal in Swift (#317)

* Adding Tree Traversal in Swift

Author: Wesley-Arrington

contents/tree_traversal/code/swift/tree.swift

@@ -0,0 +1,104 @@
+class Node {
+    var value: Int
+    var children: [Node]?
+
+    init(value: Int, children: [Node]) {
+        self.value = value
+        self.children = children
+    }
+}
+
+func createTree(numRows: Int, numChildren: Int) -> Node {
+    let node = Node(value: numRows, children: [])
+
+    if numRows > 0 {
+        for _ in 1...numChildren {
+            let child = createTree(numRows: numRows-1, numChildren: numChildren)
+            node.children?.append(child)
+        }
+    }
+
+    return node
+}
+
+func dfsRecursive(node: Node) {
+    print(node.value)
+
+    for child in node.children! {
+        dfsRecursive(node: child)
+    }
+}
+
+func dfsRecursivePostOrder(node: Node) {
+    for child in node.children! {
+        dfsRecursivePostOrder(node: child)
+    }
+
+    print(node.value)
+}
+
+func dfsRecursiveInOrderBinary(node: Node) {
+    if node.children?.count == 2 {
+        dfsRecursiveInOrderBinary(node: node.children![0])
+        print(node.value)
+        dfsRecursiveInOrderBinary(node: node.children![1])
+    } else if node.children?.count == 1 {
+        dfsRecursiveInOrderBinary(node: node.children![0])
+        print(node.value)
+    } else if node.children?.count == 0 {
+        print(node.value)
+    } else {
+        print("Not a binary tree!")
+    }
+}
+
+func dfsStack(node: Node) {
+    var stack = [node]
+    var temp: Node
+
+    while stack.count > 0 {
+        temp = stack.popLast()!
+        print(temp.value)
+
+        for child in temp.children! {
+            stack.append(child)
+        }
+    }
+}
+
+func bfsQueue(node: Node) {
+    var queue = [node]
+    var temp: Node
+
+    while queue.count > 0 {
+        temp = queue.remove(at: 0)
+        print(temp.value)
+
+        for child in temp.children! {
+            queue.append(child)
+        }
+    }
+}
+
+func main() {
+    let root = createTree(numRows: 3, numChildren: 3)
+
+    print("Using recursive DFS:")
+    dfsRecursive(node: root)
+    
+    print("Using recursive postorder DFS:")
+    dfsRecursivePostOrder(node: root)
+
+    print("Using stack-based DFS:")
+    dfsStack(node: root)
+
+    print("Using queue-based BFS:")
+    bfsQueue(node: root)
+
+    let rootBinary = createTree(numRows: 3, numChildren: 2)
+
+    print("Using In-order DFS:")
+    dfsRecursiveInOrderBinary(node: rootBinary)
+}
+
+main()

contents/tree_traversal/tree_traversal.md

@@ -26,6 +26,8 @@ This has not been implemented in your chosen language, so here is the Julia code
 [import:4-7, lang:"rust"](code/rust/tree.rs)
 {% sample lang="hs"%}
 [import:1-3, lang:"haskell"](code/haskell/TreeTraversal.hs)
+{% sample lang="swift"%}
+[import:1-9, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}
 
 Because of this, the most straightforward way to traverse the tree might be recursive. This naturally leads us to the Depth-First Search (DFS) method:
@@ -54,6 +56,8 @@ Because of this, the most straightforward way to traverse the tree might be recu
 [import:9-15 lang:"rust"](code/rust/tree.rs)
 {% sample lang="hs"%}
 [import:5-6, lang:"haskell"](code/haskell/TreeTraversal.hs)
+{% sample lang="swift"%}
+[import:24-30, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}
 
 At least to me, this makes a lot of sense. We fight recursion with recursion! First, we first output the node we are on and then we call `DFS_recursive(...)` on each of its children nodes. This method of tree traversal does what its name implies: it goes to the depths of the tree first before going through the rest of the branches. In this case, the ordering looks like:
@@ -91,6 +95,8 @@ This has not been implemented in your chosen language, so here is the Julia code
 [import:17-23, lang:"rust"](code/rust/tree.rs)
 {% sample lang="hs"%}
 [import:8-9, lang:"haskell"](code/haskell/TreeTraversal.hs)
+{% sample lang="swift"%}
+[import:32-38, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}
 
 <p>
@@ -123,6 +129,8 @@ This has not been implemented in your chosen language, so here is the Julia code
 [import:25-38, lang:"rust"](code/rust/tree.rs)
 {% sample lang="hs"%}
 [import:11-15, lang:"haskell"](code/haskell/TreeTraversal.hs)
+{% sample lang="swift"%}
+[import:40-53, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}
 
 <p>
@@ -165,6 +173,8 @@ In code, it looks like this:
 {% 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)
+{% sample lang="swift"%}
+[import:55-67, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}
 
 All this said, there are a few details about DFS that might not be idea, depending on the situation. For example, if we use DFS on an incredibly long tree, we will spend a lot of time going further and further down a single branch without searching the rest of the data structure. In addition, it is not the natural way humans would order a tree if asked to number all the nodes from top to bottom. I would argue a more natural traversal order would look something like this:
@@ -198,6 +208,8 @@ And this is exactly what Breadth-First Search (BFS) does! On top of that, it can
 [import:49-57, lang:"rust"](code/rust/tree.rs)
 {% sample lang="hs"%}
 [import:17-20, lang:"haskell"](code/haskell/TreeTraversal.hs)
+{% sample lang="swift"%}
+[import:69-81, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}
 
 ## Example Code
@@ -233,6 +245,8 @@ The code snippets were taken from this [Scratch project](https://scratch.mit.edu
 [import, lang:"rust"](code/rust/tree.rs)
 {% sample lang="hs"%}
 [import, lang:"haskell"](code/haskell/TreeTraversal.hs)
+{% sample lang="swift"%}
+[import, lang:"swift"](code/swift/tree.swift)
 {% endmethod %}