From 2c4d334dc3f11781393d354773fbb681d7c98794 Mon Sep 17 00:00:00 2001
From: soufiane-cheouati <46105138+soufiane-cheouati@users.noreply.github.com>
Date: Fri, 8 Mar 2019 22:30:42 +0000
Subject: [PATCH] Reversing binary tree classes (#6467)

* Add files via upload

* Add files via upload

* Add files via upload
---
 .../algorithms/reversingtree/TreeNode.java    | 42 ++++++++++++
 .../reversingtree/TreeReverser.java           | 68 +++++++++++++++++++
 .../reversingtree/TreeReverserUnitTest.java   | 33 +++++++++
 3 files changed, 143 insertions(+)
 create mode 100644 algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeNode.java
 create mode 100644 algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeReverser.java
 create mode 100644 algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/reversingtree/TreeReverserUnitTest.java

diff --git a/algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeNode.java b/algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeNode.java
new file mode 100644
index 0000000000..7905b752a9
--- /dev/null
+++ b/algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeNode.java
@@ -0,0 +1,42 @@
+package com.baeldung.algorithms.reversingtree;
+
+public class TreeNode {
+
+    private int value;
+    private TreeNode rightChild;
+    private TreeNode leftChild;
+
+    public int getValue() {
+        return value;
+    }
+
+    public void setValue(int value) {
+        this.value = value;
+    }
+
+    public TreeNode getRightChild() {
+        return rightChild;
+    }
+
+    public void setRightChild(TreeNode rightChild) {
+        this.rightChild = rightChild;
+    }
+
+    public TreeNode getLeftChild() {
+        return leftChild;
+    }
+
+    public void setLeftChild(TreeNode leftChild) {
+        this.leftChild = leftChild;
+    }
+
+    public TreeNode(int value, TreeNode rightChild, TreeNode leftChild) {
+        this.value = value;
+        this.rightChild = rightChild;
+        this.leftChild = leftChild;
+    }
+
+    public TreeNode(int value) {
+        this.value = value;
+    }
+}
diff --git a/algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeReverser.java b/algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeReverser.java
new file mode 100644
index 0000000000..6d3a9ddd31
--- /dev/null
+++ b/algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeReverser.java
@@ -0,0 +1,68 @@
+package com.baeldung.algorithms.reversingtree;
+
+import java.util.LinkedList;
+
+public class TreeReverser {
+
+    public TreeNode createBinaryTree() {
+
+        TreeNode leaf1 = new TreeNode(3);
+        TreeNode leaf2 = new TreeNode(1);
+        TreeNode leaf3 = new TreeNode(9);
+        TreeNode leaf4 = new TreeNode(6);
+
+        TreeNode nodeLeft = new TreeNode(2, leaf1, leaf2);
+        TreeNode nodeRight = new TreeNode(7, leaf3, leaf4);
+
+        TreeNode root = new TreeNode(4, nodeRight, nodeLeft);
+
+        return root;
+    }
+
+    public void reverseRecursive(TreeNode treeNode) {
+        if (treeNode == null) {
+            return;
+        }
+
+        TreeNode temp = treeNode.getLeftChild();
+        treeNode.setLeftChild(treeNode.getRightChild());
+        treeNode.setRightChild(temp);
+
+        reverseRecursive(treeNode.getLeftChild());
+        reverseRecursive(treeNode.getRightChild());
+    }
+
+    public void reverseIterative(TreeNode treeNode) {
+        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
+
+        if (treeNode != null) {
+            queue.add(treeNode);
+        }
+
+        while (!queue.isEmpty()) {
+
+            TreeNode node = queue.poll();
+            if (node.getLeftChild() != null)
+                queue.add(node.getLeftChild());
+            if (node.getRightChild() != null)
+                queue.add(node.getRightChild());
+
+            TreeNode temp = node.getLeftChild();
+            node.setLeftChild(node.getRightChild());
+            node.setRightChild(temp);
+        }
+    }
+
+    public String toString(TreeNode root) {
+        if (root == null) {
+            return "";
+        }
+
+        StringBuffer buffer = new StringBuffer(String.valueOf(root.getValue())).append(" ");
+
+        buffer.append(toString(root.getLeftChild()));
+        buffer.append(toString(root.getRightChild()));
+
+        return buffer.toString();
+    }
+}
diff --git a/algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/reversingtree/TreeReverserUnitTest.java b/algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/reversingtree/TreeReverserUnitTest.java
new file mode 100644
index 0000000000..cbc265fae1
--- /dev/null
+++ b/algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/reversingtree/TreeReverserUnitTest.java
@@ -0,0 +1,33 @@
+package com.baeldung.algorithms.reversingtree;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class TreeReverserUnitTest {
+
+    @Test
+    public void givenTreeWhenReversingRecursivelyThenReversed() {
+        TreeReverser reverser = new TreeReverser();
+
+        TreeNode treeNode = reverser.createBinaryTree();
+
+        reverser.reverseRecursive(treeNode);
+
+        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
+            .trim());
+    }
+
+    @Test
+    public void givenTreeWhenReversingIterativelyThenReversed() {
+        TreeReverser reverser = new TreeReverser();
+
+        TreeNode treeNode = reverser.createBinaryTree();
+
+        reverser.reverseIterative(treeNode);
+
+        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
+            .trim());
+    }
+
+}