solve

Author: sonjh1217

serialize-and-deserialize-binary-tree/sonjh1217.swift

@@ -0,0 +1,87 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.left = nil
+ *         self.right = nil
+ *     }
+ * }
+ */
+
+class Codec {
+    // O(n) time / O(n) space
+    func serialize(_ root: TreeNode?) -> String {
+        var serializedNodes = [String]()
+        var queueNodes = [TreeNode?]()
+        queueNodes.append(root)
+        var head = 0
+        
+        while head < queueNodes.count {
+            let node = queueNodes[head]
+            head += 1
+            
+            if let node {
+                serializedNodes.append("\(node.val)")
+
+                queueNodes.append(node.left)
+                queueNodes.append(node.right)
+            } else {
+                serializedNodes.append("null")
+            }
+            
+        }
+        
+        return serializedNodes.joined(separator: ",")
+    }
+    
+    // O(n) time / O(n) space
+    func deserialize(_ data: String) -> TreeNode? {
+        let serializedTree = data
+        var nodeVals = serializedTree.split(separator: ",")
+        
+        guard let first = nodeVals.first,
+           let firstVal = Int(first) else {
+            return nil
+        }
+        
+        let root = TreeNode(firstVal)
+        var queueNodes = [TreeNode]()
+        queueNodes.append(root)
+        var head = 0
+        var isLeft = true
+        
+        for i in 1..<nodeVals.count {
+            let node = queueNodes[head]
+            let stringValue = nodeVals[i]
+            let val = Int(stringValue)
+            
+            if isLeft {
+                if let val {
+                    let leftNode = TreeNode(val)
+                    node.left = leftNode
+                    queueNodes.append(leftNode)
+                } else {
+                    node.left = nil
+                }
+            } else {
+                if let val {
+                    let rightNode = TreeNode(val)
+                    node.right = rightNode
+                    queueNodes.append(rightNode)
+                } else {
+                    node.right = nil
+                }
+                head += 1
+            }
+            isLeft.toggle()
+        }
+        
+        return root
+    }
+}
+
+