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Merge branch 'master' into feature/bitwiseAnd-in-range
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‎DIRECTORY.md

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* [MaximumMinimumWindow](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/MaximumMinimumWindow.java)
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* [NextGreaterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextGreaterElement.java)
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* [NextSmallerElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextSmallerElement.java)
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* [PostfixEvaluator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixEvaluator.java)
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* [PostfixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixToInfix.java)
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* [PrefixEvaluator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java)
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* [PrefixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PrefixToInfix.java)
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* [SortStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/SortStack.java)
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* [StackPostfixNotation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/StackPostfixNotation.java)
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* [LargestRectangleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/LargestRectangleTest.java)
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* [NextGreaterElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/NextGreaterElementTest.java)
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* [NextSmallerElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/NextSmallerElementTest.java)
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* [PostfixEvaluatorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PostfixEvaluatorTest.java)
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* [PostfixToInfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PostfixToInfixTest.java)
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* [PrefixEvaluatorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java)
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* [PrefixToInfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PrefixToInfixTest.java)
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* [SortStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/SortStackTest.java)
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* [StackPostfixNotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/StackPostfixNotationTest.java)

‎src/main/java/com/thealgorithms/stacks/PostfixEvaluator.java

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package com.thealgorithms.stacks;
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import java.util.Set;
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import java.util.Stack;
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/**
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* Evaluate a postfix (Reverse Polish) expression using a stack.
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*
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* <p>Example: Expression "5 6 + 2 *" results in 22.
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* <p>Applications: Used in calculators and expression evaluation in compilers.
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*
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* @author Hardvan
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*/
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public final class PostfixEvaluator {
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private PostfixEvaluator() {
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}
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private static final Set<String> OPERATORS = Set.of("+", "-", "*", "/");
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/**
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* Evaluates the given postfix expression and returns the result.
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*
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* @param expression The postfix expression as a string with operands and operators separated by spaces.
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* @return The result of evaluating the postfix expression.
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* @throws IllegalArgumentException if the expression is invalid.
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*/
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public static int evaluatePostfix(String expression) {
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Stack<Integer> stack = new Stack<>();
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for (String token : expression.split("\\s+")) {
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if (isOperator(token)) {
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int operand2 = stack.pop();
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int operand1 = stack.pop();
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stack.push(applyOperator(token, operand1, operand2));
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} else {
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stack.push(Integer.valueOf(token));
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}
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}
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if (stack.size() != 1) {
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throw new IllegalArgumentException("Invalid expression");
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}
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return stack.pop();
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}
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/**
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* Checks if the given token is an operator.
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*
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* @param token The token to check.
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* @return true if the token is an operator, false otherwise.
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*/
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private static boolean isOperator(String token) {
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return OPERATORS.contains(token);
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}
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/**
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* Applies the given operator to the two operands.
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*
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* @param operator The operator to apply.
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* @param a The first operand.
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* @param b The second operand.
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* @return The result of applying the operator to the operands.
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*/
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private static int applyOperator(String operator, int a, int b) {
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return switch (operator) {
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case "+" -> a + b;
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case "-" -> a - b;
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case "*" -> a * b;
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case "/" -> a / b;
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default -> throw new IllegalArgumentException("Invalid operator");
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};
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}
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}

‎src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java

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package com.thealgorithms.stacks;
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import java.util.Set;
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import java.util.Stack;
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/**
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* Evaluate a prefix (Polish) expression using a stack.
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*
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* <p>Example: Expression "+ * 2 3 4" results in 10.
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* <p>Applications: Useful for implementing compilers and interpreters.
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*
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* @author Hardvan
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*/
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public final class PrefixEvaluator {
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private PrefixEvaluator() {
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}
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private static final Set<String> OPERATORS = Set.of("+", "-", "*", "/");
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/**
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* Evaluates the given prefix expression and returns the result.
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*
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* @param expression The prefix expression as a string with operands and operators separated by spaces.
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* @return The result of evaluating the prefix expression.
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* @throws IllegalArgumentException if the expression is invalid.
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*/
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public static int evaluatePrefix(String expression) {
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Stack<Integer> stack = new Stack<>();
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String[] tokens = expression.split("\\s+");
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for (int i = tokens.length - 1; i >= 0; i--) {
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String token = tokens[i];
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if (isOperator(token)) {
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int operand1 = stack.pop();
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int operand2 = stack.pop();
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stack.push(applyOperator(token, operand1, operand2));
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} else {
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stack.push(Integer.valueOf(token));
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}
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}
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if (stack.size() != 1) {
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throw new IllegalArgumentException("Invalid expression");
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}
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return stack.pop();
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}
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/**
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* Checks if the given token is an operator.
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*
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* @param token The token to check.
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* @return true if the token is an operator, false otherwise.
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*/
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private static boolean isOperator(String token) {
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return OPERATORS.contains(token);
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}
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/**
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* Applies the given operator to the two operands.
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*
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* @param operator The operator to apply.
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* @param a The first operand.
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* @param b The second operand.
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* @return The result of applying the operator to the operands.
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*/
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private static int applyOperator(String operator, int a, int b) {
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return switch (operator) {
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case "+" -> a + b;
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case "-" -> a - b;
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case "*" -> a * b;
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case "/" -> a / b;
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default -> throw new IllegalArgumentException("Invalid operator");
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};
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}
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}

‎src/test/java/com/thealgorithms/stacks/PostfixEvaluatorTest.java

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package com.thealgorithms.stacks;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import java.util.EmptyStackException;
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import org.junit.jupiter.api.Test;
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public class PostfixEvaluatorTest {
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@Test
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public void testValidExpressions() {
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assertEquals(22, PostfixEvaluator.evaluatePostfix("5 6 + 2 *"));
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assertEquals(27, PostfixEvaluator.evaluatePostfix("7 2 + 3 *"));
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assertEquals(3, PostfixEvaluator.evaluatePostfix("10 5 / 1 +"));
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}
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@Test
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public void testInvalidExpression() {
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assertThrows(EmptyStackException.class, () -> PostfixEvaluator.evaluatePostfix("5 +"));
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}
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@Test
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public void testMoreThanOneStackSizeAfterEvaluation() {
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assertThrows(IllegalArgumentException.class, () -> PostfixEvaluator.evaluatePostfix("5 6 + 2 * 3"));
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}
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}

‎src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java

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package com.thealgorithms.stacks;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import java.util.EmptyStackException;
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import org.junit.jupiter.api.Test;
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public class PrefixEvaluatorTest {
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@Test
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public void testValidExpressions() {
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assertEquals(10, PrefixEvaluator.evaluatePrefix("+ * 2 3 4"));
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assertEquals(5, PrefixEvaluator.evaluatePrefix("- + 7 3 5"));
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assertEquals(6, PrefixEvaluator.evaluatePrefix("/ * 3 2 1"));
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}
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@Test
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public void testInvalidExpression() {
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assertThrows(EmptyStackException.class, () -> PrefixEvaluator.evaluatePrefix("+ 3"));
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}
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@Test
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public void testMoreThanOneStackSizeAfterEvaluation() {
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assertThrows(IllegalArgumentException.class, () -> PrefixEvaluator.evaluatePrefix("+ 3 4 5"));
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}
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}

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