serialize and deserialize binary tree

Author: eunhwa99

serialize-and-deserialize-binary-tree/eunhwa99.kt

@@ -0,0 +1,41 @@
+package leetcode_study
+
+class Codec {
+    private var index = 0
+    // Time Complexity: O(n)
+    // Space Complexity: O(n)
+    fun serialize(root: TreeNode?): String {
+        return buildString {
+            traverse(root, this)
+        }
+    }
+
+    fun traverse(node: TreeNode?, sb: StringBuilder) {
+        if (node == null) {
+            sb.append("null,")
+            return
+        }
+        sb.append("${node.`val`},")
+        traverse(node.left, sb)
+        traverse(node.right, sb)
+    }
+
+    // Time Complexity: O(n)
+    // Space Complexity: O(n)
+    fun deserialize(data: String): TreeNode? {
+        val values = data.split(",").filter { it.isNotEmpty() }.toList()
+        index = 0
+        return buildTree(values)
+    }
+
+    fun buildTree(values: List<String>): TreeNode? {
+        if (index >= values.size) return null
+        val value = values[index++] // index 는 매개변수가 아니라 전역으로 두어야 한다!!
+        if (value == "null") return null
+        val node = TreeNode(value.toInt())
+        node.left = buildTree(values)
+        node.right = buildTree(values)
+        return node
+    }
+}
+