Encode and Decode A Binary Tree

Encode and Decode A Binary Tree

Author: remlostime

Encode and Decode Tree/EncodeAndDecodeTree.playground/Contents.swift

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+//: Playground - noun: a place where people can play
+
+
+func printTree(_ root: TreeNode?) {
+    guard let root = root else {
+        return
+    }
+
+    var pointer = root
+
+    let leftVal = root.left == nil ? "nil" : root.left!.val
+    let rightVal = root.right == nil ? "nil" : root.right!.val
+
+    print("val: \(root.val) left: \(leftVal) right: \(rightVal)")
+
+    printTree(root.left)
+    printTree(root.right)
+}
+
+let s = EncodeAndDecodeTree()
+
+let node1 = TreeNode("a")
+let node2 = TreeNode("b")
+let node3 = TreeNode("c")
+let node4 = TreeNode("d")
+let node5 = TreeNode("e")
+
+node1.left = node2
+node1.right = node3
+node3.left = node4
+node3.right = node5
+
+let encodeStr = s.encode(node1)
+print(encodeStr)
+// "a b # # c d # # e # #"
+
+
+let root = s.decode(encodeStr)
+print("Tree:")
+printTree(root)
+/*
+ Tree:
+ val: a left: b right: c
+ val: b left: nil right: nil
+ val: c left: d right: e
+ val: d left: nil right: nil
+ val: e left: nil right: nil
+ */
+

Encode and Decode Tree/EncodeAndDecodeTree.playground/Sources/EncodeAndDecodeTree.swift

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+//
+//  EncodeAndDecodeTree.swift
+//  
+//
+//  Created by Kai Chen on 19/07/2017.
+//
+//
+
+import Foundation
+
+public class TreeNode {
+    public var val: String
+    public var left: TreeNode?
+    public var right: TreeNode?
+
+    public init(_ val: String, left: TreeNode? = nil, right: TreeNode? = nil) {
+        self.val = val
+        self.left = left
+        self.right = right
+    }
+}
+
+public class EncodeAndDecodeTree {
+    private var encodeStr = ""
+    private var ret: [String] = []
+
+    public init() {}
+
+    public func encode(_ root: TreeNode?) -> String {
+        encodeIt(root)
+
+        return encodeStr
+    }
+
+    public func decode(_ data: String) -> TreeNode? {
+        var s = data
+        while (s.contains(" ")) {
+            let index = s.index(of: " ")
+            let endIndex = s.index(before: index)
+            let element = s[s.startIndex...endIndex]
+            ret.append(element)
+            let range = ClosedRange(uncheckedBounds: (lower: s.startIndex, upper: index))
+            s.removeSubrange(range)
+        }
+
+        if ret.count == 0 {
+            return nil
+        }
+
+        var dep = 0
+        let root = decodeIt(&dep)
+
+        return root
+    }
+
+    private func getNode(_ element: String) -> TreeNode? {
+        if element == "#" {
+            return nil
+        }
+
+        return TreeNode(element)
+    }
+
+    private func decodeIt(_ dep: inout Int) -> TreeNode? {
+        guard let currentNode = getNode(ret[dep]) else {
+            return nil
+        }
+
+        dep += 1
+        let left = decodeIt(&dep)
+        dep += 1
+        let right = decodeIt(&dep)
+
+        currentNode.left = left
+        currentNode.right = right
+
+        return currentNode
+    }
+
+    private func encodeIt(_ root: TreeNode?) {
+        guard let root = root else {
+            encodeStr += "# "
+            return
+        }
+
+        encodeStr += root.val + " "
+        encodeIt(root.left)
+        encodeIt(root.right)
+    }
+}
+
+extension String {
+    func index(of target: Character) -> String.Index {
+        var i = 0
+        for c in self.characters {
+            if c == target {
+                return self.index(self.startIndex, offsetBy: i)
+            }
+            i += 1
+        }
+
+        return self.endIndex
+    }
+}

Encode and Decode Tree/EncodeAndDecodeTree.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Encode and Decode Tree/EncodeAndDecodeTree.swift

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+//
+//  EncodeAndDecodeTree.swift
+//
+//
+//  Created by Kai Chen on 19/07/2017.
+//
+//
+
+import Foundation
+
+public class TreeNode {
+    public var val: String
+    public var left: TreeNode?
+    public var right: TreeNode?
+
+    public init(_ val: String, left: TreeNode? = nil, right: TreeNode? = nil) {
+        self.val = val
+        self.left = left
+        self.right = right
+    }
+}
+
+public class EncodeAndDecodeTree {
+    private var encodeStr = ""
+    private var ret: [String] = []
+
+    public init() {}
+
+    public func encode(_ root: TreeNode?) -> String {
+        encodeIt(root)
+
+        return encodeStr
+    }
+
+    public func decode(_ data: String) -> TreeNode? {
+        var s = data
+        while (s.contains(" ")) {
+            let index = s.index(of: " ")
+            let endIndex = s.index(before: index)
+            let element = s[s.startIndex...endIndex]
+            ret.append(element)
+            let range = ClosedRange(uncheckedBounds: (lower: s.startIndex, upper: index))
+            s.removeSubrange(range)
+        }
+
+        if ret.count == 0 {
+            return nil
+        }
+
+        var dep = 0
+        let root = decodeIt(&dep)
+
+        return root
+    }
+
+    private func getNode(_ element: String) -> TreeNode? {
+        if element == "#" {
+            return nil
+        }
+
+        return TreeNode(element)
+    }
+
+    private func decodeIt(_ dep: inout Int) -> TreeNode? {
+        guard let currentNode = getNode(ret[dep]) else {
+            return nil
+        }
+
+        dep += 1
+        let left = decodeIt(&dep)
+        dep += 1
+        let right = decodeIt(&dep)
+
+        currentNode.left = left
+        currentNode.right = right
+
+        return currentNode
+    }
+
+    private func encodeIt(_ root: TreeNode?) {
+        guard let root = root else {
+            encodeStr += "# "
+            return
+        }
+
+        encodeStr += root.val + " "
+        encodeIt(root.left)
+        encodeIt(root.right)
+    }
+}
+
+extension String {
+    func index(of target: Character) -> String.Index {
+        var i = 0
+        for c in self.characters {
+            if c == target {
+                return self.index(self.startIndex, offsetBy: i)
+            }
+            i += 1
+        }
+        
+        return self.endIndex
+    }
+}

Encode and Decode Tree/readme.md

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+# Encode and Decode Binary Tree
+
+We need to design an algorithm to encode and decode a binary tree. 
+* **Encode**: Convert a tree into a string that can be stored in the disk.
+* **Decode**: Given the encoded string, you need to convert it into a Tree.
+
+For example, you may serialize the following tree
+
+
+as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.
+Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
+
+## Solution
+For example, given a tree like this
+>       a
+>      /  \\
+>
+>    b     c
+>
+>    ​      /  \\
+>    ​    d    e
+
+We can use inorder traversal to convert the tree into the string like this `a b # # c d # # e # #`
+
+So, the idea is for the empty node, we use `#` to represent.
+
+For the decode process, we can still use inorder to convert the string back to a tree.