Add tree traversal

Author: Romanow

src/main/kotlin/ru/romanow/algorithms/InOrderDeepFirstSearch.kt

@@ -3,12 +3,19 @@ package ru.romanow.algorithms
 import ru.romanow.models.TreeNode
 
 class InOrderDeepFirstSearch {
-    fun traverse(node: TreeNode?): List<Int> {
+    fun traverse(root: TreeNode?): List<Int> {
+        val result = mutableListOf<Int>()
+        traverse(root, result)
+        return result
+    }
+
+    private fun traverse(node: TreeNode?, accumulator: MutableList<Int>) {
         if (node == null) {
-            return emptyList()
+            return
         }
-        return traverse(node.left) +
-            listOf(node.value) +
-            traverse(node.right)
+        traverse(node.left, accumulator)
+        // print("${node.value} ")
+        accumulator.add(node.value)
+        traverse(node.right, accumulator)
     }
 }

src/main/kotlin/ru/romanow/algorithms/PostOrderDeepFirstSearch.kt

@@ -3,12 +3,19 @@ package ru.romanow.algorithms
 import ru.romanow.models.TreeNode
 
 class PostOrderDeepFirstSearch {
-    fun traverse(node: TreeNode?): List<Int> {
+    fun traverse(root: TreeNode?): List<Int> {
+        val result = mutableListOf<Int>()
+        traverse(root, result)
+        return result
+    }
+
+    private fun traverse(node: TreeNode?, accumulator: MutableList<Int>) {
         if (node == null) {
-            return emptyList()
+            return
         }
-        return traverse(node.right) +
-            traverse(node.left) +
-            listOf(node.value)
+        traverse(node.left, accumulator)
+        traverse(node.right, accumulator)
+        // print("${node.value} ")
+        accumulator.add(node.value)
     }
 }

src/main/kotlin/ru/romanow/algorithms/PreOrderDeepFirstSearch.kt

@@ -3,12 +3,19 @@ package ru.romanow.algorithms
 import ru.romanow.models.TreeNode
 
 class PreOrderDeepFirstSearch {
-    fun traverse(node: TreeNode?): List<Int> {
+    fun traverse(root: TreeNode?): List<Int> {
+        val result = mutableListOf<Int>()
+        traverse(root, result)
+        return result
+    }
+
+    private fun traverse(node: TreeNode?, accumulator: MutableList<Int>) {
         if (node == null) {
-            return emptyList()
+            return
         }
-        return listOf(node.value) +
-            traverse(node.left) +
-            traverse(node.right)
+        // print("${node.value} ")
+        accumulator.add(node.value)
+        traverse(node.left, accumulator)
+        traverse(node.right, accumulator)
     }
 }

src/test/kotlin/ru/romanow/algorithms/PostOrderDeepFirstSearchTest.kt

@@ -24,6 +24,6 @@ class PostOrderDeepFirstSearchTest {
 
     internal class ValueProvider : ArgumentsProvider {
         override fun provideArguments(context: ExtensionContext): Stream<Arguments> =
-            Stream.of(Arguments.of(listOf(10, 5, 15, 3, 7, 12, 20), listOf(20, 12, 15, 7, 3, 5, 10)))
+            Stream.of(Arguments.of(listOf(10, 5, 15, 3, 7, 12, 20), listOf(3, 7, 5, 12, 20, 15, 10)))
     }
 }