Add Serialize and Deserialize a BinaryTree

Author: marttp

kotlin/Trees/SerializeAndDeserializeABinaryTree.kt

@@ -0,0 +1,57 @@
+import java.util.LinkedList
+import ds.TreeNode
+
+/*
+    Definition of TreeNode:
+
+    data class TreeNode(
+        var value: Int,
+        var left: TreeNode? = null,
+        var right: TreeNode? = null
+    )
+*/
+
+fun serialize(root: TreeNode?): String {
+    // Perform a preorder traversal to add node values to a list, then convert the
+    // list to a string.
+    val serializedList = mutableListOf<String>()
+    preorderSerialize(root, serializedList)
+    // Convert the list to a string and separate each value using a comma
+    // delimiter.
+    return serializedList.joinToString(",")
+}
+
+// Helper function to perform serialization through preorder traversal.
+fun preorderSerialize(node: TreeNode?, serializedList: MutableList<String>) {
+    // Base case: mark null nodes as '#'.
+    if (node == null) {
+        serializedList.add("#")
+        return
+    }
+    // Preorder traversal processes the current node first, then the left and right
+    // children.
+    serializedList.add(node.value.toString())
+    preorderSerialize(node.left, serializedList)
+    preorderSerialize(node.right, serializedList)
+}
+
+fun deserialize(data: String): TreeNode? {
+    // Obtain the node values by splitting the string using the comma delimiter.
+    val nodeValues = LinkedList<String>(data.split(","))
+    return buildTree(nodeValues)
+}
+
+// Helper function to construct the tree using preorder traversal.
+fun buildTree(values: LinkedList<String>): TreeNode? {
+    val value = values.poll()
+    // Base case: '#' indicates a null node.
+    if (value == "#") {
+        return null
+    }
+    // Use preorder traversal processes the current node first, then the left and
+    // right children.
+    val node = TreeNode(value.toInt())
+    node.left = buildTree(values)
+    node.right = buildTree(values)
+    return node
+}