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Merged
siriak merged 2 commits into from
Feb 25, 2023
Merged

Added recursive&iterative inorder binary tree traversal #3898

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114d027
Added recursive& iterative inorder binary tree traversal
albina-astr Feb 21, 2023
535e6aa
Merge branch 'master' into inorder-traversal
siriak Feb 25, 2023
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60 changes: 60 additions & 0 deletions src/main/java/com/thealgorithms/datastructures/trees/InorderTraversal.java
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package com.thealgorithms.datastructures.trees;

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.List;

/**
* Given tree is traversed in an 'inorder' way: LEFT -> ROOT -> RIGHT.
* Below are given the recursive and iterative implementations.
*
* Complexities:
* Recursive: O(n) - time, O(n) - space, where 'n' is the number of nodes in a tree.
*
* Iterative: O(n) - time, O(h) - space, where 'n' is the number of nodes in a tree
* and 'h' is the height of a binary tree.
* In the worst case 'h' can be O(n) if tree is completely unbalanced, for instance:
* 5
* \
* 6
* \
* 7
* \
* 8
*
* @author Albina Gimaletdinova on 21/02/2023
*/
public class InorderTraversal {
public static List<Integer> recursiveInorder(BinaryTree.Node root) {
List<Integer> result = new ArrayList<>();
recursiveInorder(root, result);
return result;
}

public static List<Integer> iterativeInorder(BinaryTree.Node root) {
List<Integer> result = new ArrayList<>();
if (root == null) return result;

Deque<BinaryTree.Node> stack = new ArrayDeque<>();
while (!stack.isEmpty() || root != null) {
while (root != null) {
stack.push(root);
root = root.left;
}
root = stack.pop();
result.add(root.data);
root = root.right;
}
return result;
}

private static void recursiveInorder(BinaryTree.Node root, List<Integer> result) {
if (root == null) {
return;
}
recursiveInorder(root.left, result);
result.add(root.data);
recursiveInorder(root.right, result);
}
}
53 changes: 53 additions & 0 deletions src/test/java/com/thealgorithms/datastructures/trees/InorderTraversalTest.java
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package com.thealgorithms.datastructures.trees;

import org.junit.jupiter.api.Test;

import java.util.Collections;
import java.util.List;

import static org.junit.jupiter.api.Assertions.assertEquals;

/**
* @author Albina Gimaletdinova on 21/02/2023
*/
public class InorderTraversalTest {
@Test
public void testNullRoot() {
assertEquals(Collections.emptyList(), InorderTraversal.recursiveInorder(null));
assertEquals(Collections.emptyList(), InorderTraversal.iterativeInorder(null));
}

/*
1
/ \
2 3
/\ /\
4 5 6 7
*/
@Test
public void testRecursiveInorder() {
final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{1, 2, 3, 4, 5, 6, 7});
List<Integer> expected = List.of(4, 2, 5, 1, 6, 3, 7);

assertEquals(expected, InorderTraversal.recursiveInorder(root));
assertEquals(expected, InorderTraversal.iterativeInorder(root));
}

/*
5
\
6
\
7
\
8
*/
@Test
public void testRecursiveInorderNonBalanced() {
final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{5, null, 6, null, 7, null, 8});
List<Integer> expected = List.of(5, 6, 7, 8);

assertEquals(expected, InorderTraversal.recursiveInorder(root));
assertEquals(expected, InorderTraversal.iterativeInorder(root));
}
}
12 changes: 8 additions & 4 deletions src/test/java/com/thealgorithms/datastructures/trees/PreOrderTraversalTest.java
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Expand Up @@ -27,8 +27,10 @@ public void testNullRoot() {
@Test
public void testRecursivePreOrder() {
final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{1, 2, 3, 4, 5, 6, 7});
assertEquals(List.of(1, 2, 4, 5, 3, 6, 7), PreOrderTraversal.recursivePreOrder(root));
assertEquals(List.of(1, 2, 4, 5, 3, 6, 7), PreOrderTraversal.iterativePreOrder(root));
List<Integer> expected = List.of(1, 2, 4, 5, 3, 6, 7);

assertEquals(expected, PreOrderTraversal.recursivePreOrder(root));
assertEquals(expected, PreOrderTraversal.iterativePreOrder(root));
}

/*
Expand All @@ -43,7 +45,9 @@ public void testRecursivePreOrder() {
@Test
public void testRecursivePreOrderNonBalanced() {
final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{5, null, 6, null, 7, null, 8});
assertEquals(List.of(5, 6, 7, 8), PreOrderTraversal.recursivePreOrder(root));
assertEquals(List.of(5, 6, 7, 8), PreOrderTraversal.iterativePreOrder(root));
List<Integer> expected = List.of(5, 6, 7, 8);

assertEquals(expected, PreOrderTraversal.recursivePreOrder(root));
assertEquals(expected, PreOrderTraversal.iterativePreOrder(root));
}
}