diff --git a/src/main/java/com/thealgorithms/datastructures/trees/SameTreesCheck.java b/src/main/java/com/thealgorithms/datastructures/trees/SameTreesCheck.java new file mode 100644 index 00000000..6a2258b5 --- /dev/null +++ b/src/main/java/com/thealgorithms/datastructures/trees/SameTreesCheck.java @@ -0,0 +1,82 @@ +package com.thealgorithms.datastructures.trees; + +import java.util.ArrayDeque; +import java.util.Deque; + +/** + * Given 2 binary trees. + * This code checks whether they are the same (structurally identical and have the same values) or not. + *

+ * Example: + * 1. Binary trees: + * 1 1 + * / \ / \ + * 2 3 2 3 + * /\ /\ /\ /\ + * 4 5 6 7 4 5 6 7 + * These trees are the same, so the code returns 'true'. + *

+ * 2. Binary trees: + * 1 1 + * / \ + * 2 2 + * These trees are NOT the same (the structure differs), so the code returns 'false'. + *

+ * This solution implements the breadth-first search (BFS) algorithm. + * For each tree we create a queue and iterate the trees using these queues. + * On each step we check the nodes for equality, and if the nodes are not the same, return false. + * Otherwise, add children nodes to the queues and continue traversing the trees. + *

+ * Complexities: + * O(N) - time, where N is the number of nodes in a binary tree, + * O(N) - space, where N is the number of nodes in a binary tree. + * + * @author Albina Gimaletdinova on 13/01/2023 + */ +public class SameTreesCheck { + public static boolean check(BinaryTree.Node p, BinaryTree.Node q) { + if (p == null && q == null) { + return true; + } + if (p == null || q == null) { + return false; + } + + Deque q1 = new ArrayDeque<>(); + Deque q2 = new ArrayDeque<>(); + q1.add(p); + q2.add(q); + while (!q1.isEmpty() && !q2.isEmpty()) { + BinaryTree.Node first = q1.poll(); + BinaryTree.Node second = q2.poll(); + // check that some node can be null + // if the check is true: both nodes are null or both nodes are not null + if (!equalNodes(first, second)) return false; + + if (first != null) { + if (!equalNodes(first.left, second.left)) return false; + if (first.left != null) { + q1.add(first.left); + q2.add(second.left); + } + + if (!equalNodes(first.right, second.right)) return false; + if (first.right != null) { + q1.add(first.right); + q2.add(second.right); + } + } + } + return true; + } + + private static boolean equalNodes(BinaryTree.Node p, BinaryTree.Node q) { + if (p == null && q == null) { + return true; + } + if (p == null || q == null) { + return false; + } + return p.data == q.data; + } +} diff --git a/src/test/java/com/thealgorithms/datastructures/trees/SameTreesCheckTest.java b/src/test/java/com/thealgorithms/datastructures/trees/SameTreesCheckTest.java new file mode 100644 index 00000000..365ee99f --- /dev/null +++ b/src/test/java/com/thealgorithms/datastructures/trees/SameTreesCheckTest.java @@ -0,0 +1,71 @@ +package com.thealgorithms.datastructures.trees; + +import org.junit.jupiter.api.Test; + +import static org.junit.jupiter.api.Assertions.assertFalse; +import static org.junit.jupiter.api.Assertions.assertTrue; + +/** + * @author Albina Gimaletdinova on 12/01/2023 + */ +public class SameTreesCheckTest { + @Test + public void testBothRootsAreNull() { + assertTrue(SameTreesCheck.check(null, null)); + } + + @Test + public void testOneRootIsNull() { + final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{100}); + assertFalse(SameTreesCheck.check(root, null)); + } + + @Test + public void testSingleNodeTreesAreSame() { + final BinaryTree.Node p = TreeTestUtils.createTree(new Integer[]{100}); + final BinaryTree.Node q = TreeTestUtils.createTree(new Integer[]{100}); + assertTrue(SameTreesCheck.check(p, q)); + } + + /* + 1 1 + / \ / \ + 2 3 2 3 + /\ /\ /\ /\ + 4 5 6 7 4 5 6 7 + */ + @Test + public void testSameTreesIsSuccessful() { + final BinaryTree.Node p = TreeTestUtils.createTree(new Integer[]{1, 2, 3, 4, 5, 6, 7}); + final BinaryTree.Node q = TreeTestUtils.createTree(new Integer[]{1, 2, 3, 4, 5, 6, 7}); + assertTrue(SameTreesCheck.check(p, q)); + } + + + /* + 1 1 + / \ / \ + 2 3 2 3 + /\ /\ /\ / + 4 5 6 7 4 5 6 + */ + @Test + public void testSameTreesFails() { + final BinaryTree.Node p = TreeTestUtils.createTree(new Integer[]{1, 2, 3, 4, 5, 6, 7}); + final BinaryTree.Node q = TreeTestUtils.createTree(new Integer[]{1, 2, 3, 4, 5, 6}); + assertFalse(SameTreesCheck.check(p, q)); + } + + /* + 1 1 + / \ + 2 2 + */ + @Test + public void testTreesWithDifferentStructure() { + final BinaryTree.Node p = TreeTestUtils.createTree(new Integer[]{1, 2}); + final BinaryTree.Node q = TreeTestUtils.createTree(new Integer[]{1, null, 2}); + assertFalse(SameTreesCheck.check(p, q)); + } +} +