diff --git a/src/main/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorder.java b/src/main/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorder.java index d99d167b..99b1fb4e 100644 --- a/src/main/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorder.java +++ b/src/main/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorder.java @@ -1,6 +1,7 @@ package com.thealgorithms.datastructures.trees; import com.thealgorithms.datastructures.trees.BinaryTree.Node; + import java.util.HashMap; import java.util.Map; @@ -11,66 +12,37 @@ import java.util.Map; * subtree. Based on that index create left and right subtree. Complexity: Time: * O(n^2) for each node there is iteration to find index in inorder array Space: * Stack size = O(height) = O(lg(n)) - * + *

* Optimized Solution: Instead of iterating over inorder array to find index of * root value, create a hashmap and find out the index of root value. * Complexity: Time: O(n) hashmap reduced iteration to find index in inorder * array Space: O(n) space taken by hashmap - * */ public class CreateBinaryTreeFromInorderPreorder { - - public static void main(String[] args) { - test(new Integer[] {}, new Integer[] {}); // empty tree - test(new Integer[] { 1 }, new Integer[] { 1 }); // single node tree - test(new Integer[] { 1, 2, 3, 4 }, new Integer[] { 1, 2, 3, 4 }); // right skewed tree - test(new Integer[] { 1, 2, 3, 4 }, new Integer[] { 4, 3, 2, 1 }); // left skewed tree - test( - new Integer[] { 3, 9, 20, 15, 7 }, - new Integer[] { 9, 3, 15, 20, 7 } - ); // normal tree + public static Node createTree(final Integer[] preorder, final Integer[] inorder) { + if (preorder == null || inorder == null) { + return null; + } + return createTree(preorder, inorder, 0, 0, inorder.length); } - private static void test( - final Integer[] preorder, - final Integer[] inorder - ) { - System.out.println( - "\n====================================================" - ); - System.out.println("Naive Solution..."); - BinaryTree root = new BinaryTree( - createTree(preorder, inorder, 0, 0, inorder.length) - ); - System.out.println("Preorder Traversal: "); - root.preOrder(root.getRoot()); - System.out.println("\nInorder Traversal: "); - root.inOrder(root.getRoot()); - System.out.println("\nPostOrder Traversal: "); - root.postOrder(root.getRoot()); - - Map map = new HashMap<>(); - for (int i = 0; i < inorder.length; i++) { - map.put(inorder[i], i); + public static Node createTreeOptimized(final Integer[] preorder, final Integer[] inorder) { + if (preorder == null || inorder == null) { + return null; } - BinaryTree optimizedRoot = new BinaryTree( - createTreeOptimized(preorder, inorder, 0, 0, inorder.length, map) - ); - System.out.println("\n\nOptimized solution..."); - System.out.println("Preorder Traversal: "); - optimizedRoot.preOrder(root.getRoot()); - System.out.println("\nInorder Traversal: "); - optimizedRoot.inOrder(root.getRoot()); - System.out.println("\nPostOrder Traversal: "); - optimizedRoot.postOrder(root.getRoot()); + Map inorderMap = new HashMap<>(); + for (int i = 0; i < inorder.length; i++) { + inorderMap.put(inorder[i], i); + } + return createTreeOptimized(preorder, inorderMap, 0, 0, inorder.length); } private static Node createTree( - final Integer[] preorder, - final Integer[] inorder, - final int preStart, - final int inStart, - final int size + final Integer[] preorder, + final Integer[] inorder, + final int preStart, + final int inStart, + final int size ) { if (size == 0) { return null; @@ -78,37 +50,36 @@ public class CreateBinaryTreeFromInorderPreorder { Node root = new Node(preorder[preStart]); int i = inStart; - while (preorder[preStart] != inorder[i]) { + while (!preorder[preStart].equals(inorder[i])) { i++; } int leftNodesCount = i - inStart; int rightNodesCount = size - leftNodesCount - 1; root.left = - createTree( - preorder, - inorder, - preStart + 1, - inStart, - leftNodesCount - ); + createTree( + preorder, + inorder, + preStart + 1, + inStart, + leftNodesCount + ); root.right = - createTree( - preorder, - inorder, - preStart + leftNodesCount + 1, - i + 1, - rightNodesCount - ); + createTree( + preorder, + inorder, + preStart + leftNodesCount + 1, + i + 1, + rightNodesCount + ); return root; } private static Node createTreeOptimized( - final Integer[] preorder, - final Integer[] inorder, - final int preStart, - final int inStart, - final int size, - final Map inorderMap + final Integer[] preorder, + final Map inorderMap, + final int preStart, + final int inStart, + final int size ) { if (size == 0) { return null; @@ -119,23 +90,21 @@ public class CreateBinaryTreeFromInorderPreorder { int leftNodesCount = i - inStart; int rightNodesCount = size - leftNodesCount - 1; root.left = - createTreeOptimized( - preorder, - inorder, - preStart + 1, - inStart, - leftNodesCount, - inorderMap - ); + createTreeOptimized( + preorder, + inorderMap, + preStart + 1, + inStart, + leftNodesCount + ); root.right = - createTreeOptimized( - preorder, - inorder, - preStart + leftNodesCount + 1, - i + 1, - rightNodesCount, - inorderMap - ); + createTreeOptimized( + preorder, + inorderMap, + preStart + leftNodesCount + 1, + i + 1, + rightNodesCount + ); return root; } } diff --git a/src/test/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorderTest.java b/src/test/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorderTest.java new file mode 100644 index 00000000..59352f54 --- /dev/null +++ b/src/test/java/com/thealgorithms/datastructures/trees/CreateBinaryTreeFromInorderPreorderTest.java @@ -0,0 +1,103 @@ +package com.thealgorithms.datastructures.trees; + +import org.junit.jupiter.api.Assertions; +import org.junit.jupiter.api.Test; + +import java.util.Arrays; + +/** + * @author Albina Gimaletdinova on 14/05/2023 + */ +public class CreateBinaryTreeFromInorderPreorderTest { + @Test + public void testOnNullArraysShouldReturnNullTree() { + // when + BinaryTree.Node root = CreateBinaryTreeFromInorderPreorder.createTree(null, null); + BinaryTree.Node rootOpt = CreateBinaryTreeFromInorderPreorder.createTreeOptimized(null, null); + + // then + Assertions.assertNull(root); + Assertions.assertNull(rootOpt); + } + + @Test + public void testOnEmptyArraysShouldCreateNullTree() { + // given + Integer[] preorder = {}; + Integer[] inorder = {}; + + // when + BinaryTree.Node root = CreateBinaryTreeFromInorderPreorder.createTree(preorder, inorder); + BinaryTree.Node rootOpt = CreateBinaryTreeFromInorderPreorder.createTreeOptimized(preorder, inorder); + + // then + Assertions.assertNull(root); + Assertions.assertNull(rootOpt); + } + + @Test + public void testOnSingleNodeTreeShouldCreateCorrectTree() { + // given + Integer[] preorder = {1}; + Integer[] inorder = {1}; + + // when + BinaryTree.Node root = CreateBinaryTreeFromInorderPreorder.createTree(preorder, inorder); + BinaryTree.Node rootOpt = CreateBinaryTreeFromInorderPreorder.createTreeOptimized(preorder, inorder); + + // then + checkTree(preorder, inorder, root); + checkTree(preorder, inorder, rootOpt); + } + + @Test + public void testOnRightSkewedTreeShouldCreateCorrectTree() { + // given + Integer[] preorder = {1, 2, 3, 4}; + Integer[] inorder = {1, 2, 3, 4}; + + // when + BinaryTree.Node root = CreateBinaryTreeFromInorderPreorder.createTree(preorder, inorder); + BinaryTree.Node rootOpt = CreateBinaryTreeFromInorderPreorder.createTreeOptimized(preorder, inorder); + + // then + checkTree(preorder, inorder, root); + checkTree(preorder, inorder, rootOpt); + } + + @Test + public void testOnLeftSkewedTreeShouldCreateCorrectTree() { + // given + Integer[] preorder = {1, 2, 3, 4}; + Integer[] inorder = {4, 3, 2, 1}; + + // when + BinaryTree.Node root = CreateBinaryTreeFromInorderPreorder.createTree(preorder, inorder); + BinaryTree.Node rootOpt = CreateBinaryTreeFromInorderPreorder.createTreeOptimized(preorder, inorder); + + // then + checkTree(preorder, inorder, root); + checkTree(preorder, inorder, rootOpt); + } + + @Test + public void testOnNormalTreeShouldCreateCorrectTree() { + // given + Integer[] preorder = {3, 9, 20, 15, 7}; + Integer[] inorder = {9, 3, 15, 20, 7}; + + // when + BinaryTree.Node root = CreateBinaryTreeFromInorderPreorder.createTree(preorder, inorder); + BinaryTree.Node rootOpt = CreateBinaryTreeFromInorderPreorder.createTreeOptimized(preorder, inorder); + + // then + checkTree(preorder, inorder, root); + checkTree(preorder, inorder, rootOpt); + } + + private static void checkTree(Integer[] preorder, Integer[] inorder, BinaryTree.Node root) { + Assertions.assertNotNull(root); + Assertions.assertEquals(PreOrderTraversal.iterativePreOrder(root), Arrays.asList(preorder)); + Assertions.assertEquals(InorderTraversal.iterativeInorder(root), Arrays.asList(inorder)); + } +}