From 7e971ce70b29558210385b8627c3e7d62c03a364 Mon Sep 17 00:00:00 2001 From: Hardik Pawar Date: Sun, 13 Oct 2024 12:23:15 +0530 Subject: [PATCH 1/4] feat: Add `PrefixEvaluator` new algorithm with Junit tests --- .../thealgorithms/stacks/PrefixEvaluator.java | 73 +++++++++++++++++++ .../stacks/PrefixEvaluatorTest.java | 28 +++++++ 2 files changed, 101 insertions(+) create mode 100644 src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java create mode 100644 src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java diff --git a/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java b/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java new file mode 100644 index 000000000000..98143b843083 --- /dev/null +++ b/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java @@ -0,0 +1,73 @@ +package com.thealgorithms.stacks; + +import java.util.Stack; + +/** + * Evaluate a prefix (Polish) expression using a stack. + * + *

Example: Expression "+ * 2 3 4" results in 10. + *

Applications: Useful for implementing compilers and interpreters. + * + * @author Hardvan + */ +public final class PrefixEvaluator { + private PrefixEvaluator() { + } + + /** + * Evaluates the given prefix expression and returns the result. + * + * @param expression The prefix expression as a string with operands and operators separated by spaces. + * @return The result of evaluating the prefix expression. + * @throws IllegalArgumentException if the expression is invalid. + */ + public static int evaluatePrefix(String expression) { + Stack stack = new Stack<>(); + String[] tokens = expression.split("\\s+"); + + for (int i = tokens.length - 1; i >= 0; i--) { + String token = tokens[i]; + if (isOperator(token)) { + int operand1 = stack.pop(); + int operand2 = stack.pop(); + stack.push(applyOperator(token, operand1, operand2)); + } else { + stack.push(Integer.parseInt(token)); + } + } + + if (stack.size() != 1) { + throw new IllegalArgumentException("Invalid expression"); + } + + return stack.pop(); + } + + /** + * Checks if the given token is an operator. + * + * @param token The token to check. + * @return true if the token is an operator, false otherwise. + */ + private static boolean isOperator(String token) { + return token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/"); + } + + /** + * Applies the given operator to the two operands. + * + * @param operator The operator to apply. + * @param a The first operand. + * @param b The second operand. + * @return The result of applying the operator to the operands. + */ + private static int applyOperator(String operator, int a, int b) { + return switch (operator) { + case "+" -> a + b; + case "-" -> a - b; + case "*" -> a * b; + case "/" -> a / b; + default -> throw new IllegalArgumentException("Invalid operator"); + }; + } +} diff --git a/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java b/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java new file mode 100644 index 000000000000..af52e0f17ee8 --- /dev/null +++ b/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java @@ -0,0 +1,28 @@ +package com.thealgorithms.stacks; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import org.junit.jupiter.api.Test; + +import java.util.EmptyStackException; + +public class PrefixEvaluatorTest { + + @Test + public void testValidExpressions() { + assertEquals(10, PrefixEvaluator.evaluatePrefix("+ * 2 3 4")); + assertEquals(5, PrefixEvaluator.evaluatePrefix("- + 7 3 5")); + assertEquals(6, PrefixEvaluator.evaluatePrefix("/ * 3 2 1")); + } + + @Test + public void testInvalidExpression() { + assertThrows(EmptyStackException.class, () -> PrefixEvaluator.evaluatePrefix("+ 3")); + } + + @Test + public void testMoreThanOneStackSizeAfterEvaluation() { + assertThrows(IllegalArgumentException.class, () -> PrefixEvaluator.evaluatePrefix("+ 3 4 5")); + } +} From 17a5009b76690c1b2853c4893b6236e8a2f1bd41 Mon Sep 17 00:00:00 2001 From: Hardvan Date: Sun, 13 Oct 2024 06:53:32 +0000 Subject: [PATCH 2/4] Update directory --- DIRECTORY.md | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/DIRECTORY.md b/DIRECTORY.md index af956a1a26ed..9f7ff1d4018c 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -26,9 +26,11 @@ * [BcdConversion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/BcdConversion.java) * [BinaryPalindromeCheck](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/BinaryPalindromeCheck.java) * [BitSwap](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/BitSwap.java) + * [BooleanAlgebraGates](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/BooleanAlgebraGates.java) * [ClearLeftmostSetBit](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/ClearLeftmostSetBit.java) * [CountLeadingZeros](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/CountLeadingZeros.java) * [CountSetBits](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/CountSetBits.java) + * [FindNthBit](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/FindNthBit.java) * [GrayCodeConversion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/GrayCodeConversion.java) * [HammingDistance](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/HammingDistance.java) * [HigherLowerPowerOfTwo](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/HigherLowerPowerOfTwo.java) @@ -55,6 +57,7 @@ * [CompositeLFSR](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/a5/CompositeLFSR.java) * [LFSR](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/a5/LFSR.java) * [Utils](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/a5/Utils.java) + * [ADFGVXCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ADFGVXCipher.java) * [AES](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AES.java) * [AESEncryption](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AESEncryption.java) * [AffineCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AffineCipher.java) @@ -134,6 +137,7 @@ * [FordFulkerson](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/FordFulkerson.java) * [Graphs](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/Graphs.java) * [HamiltonianCycle](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/HamiltonianCycle.java) + * [JohnsonsAlgorithm](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/JohnsonsAlgorithm.java) * [KahnsAlgorithm](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/KahnsAlgorithm.java) * [Kosaraju](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/Kosaraju.java) * [Kruskal](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/graphs/Kruskal.java) @@ -341,6 +345,7 @@ * [EulersFunction](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/EulersFunction.java) * [Factorial](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/Factorial.java) * [FactorialRecursion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FactorialRecursion.java) + * [FastExponentiation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FastExponentiation.java) * [FastInverseSqrt](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FastInverseSqrt.java) * [FFT](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FFT.java) * [FFTBluestein](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FFTBluestein.java) @@ -593,6 +598,7 @@ * [NextGreaterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextGreaterElement.java) * [NextSmallerElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextSmallerElement.java) * [PostfixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixToInfix.java) + * [PrefixEvaluator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java) * [PrefixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PrefixToInfix.java) * [SortStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/SortStack.java) * [StackPostfixNotation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/StackPostfixNotation.java) @@ -658,9 +664,11 @@ * [BcdConversionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/BcdConversionTest.java) * [BinaryPalindromeCheckTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/BinaryPalindromeCheckTest.java) * [BitSwapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/BitSwapTest.java) + * [BooleanAlgebraGatesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/BooleanAlgebraGatesTest.java) * [ClearLeftmostSetBitTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/ClearLeftmostSetBitTest.java) * [CountLeadingZerosTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/CountLeadingZerosTest.java) * [CountSetBitsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/CountSetBitsTest.java) + * [FindNthBitTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/FindNthBitTest.java) * [GrayCodeConversionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/GrayCodeConversionTest.java) * [HammingDistanceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/HammingDistanceTest.java) * [HigherLowerPowerOfTwoTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/HigherLowerPowerOfTwoTest.java) @@ -684,6 +692,7 @@ * [A5CipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/a5/A5CipherTest.java) * [A5KeyStreamGeneratorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/a5/A5KeyStreamGeneratorTest.java) * [LFSRTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/a5/LFSRTest.java) + * [ADFGVXCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/ADFGVXCipherTest.java) * [AESEncryptionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AESEncryptionTest.java) * [AffineCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AffineCipherTest.java) * [AtbashTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AtbashTest.java) @@ -752,6 +761,7 @@ * [FloydWarshallTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/FloydWarshallTest.java) * [FordFulkersonTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/FordFulkersonTest.java) * [HamiltonianCycleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/HamiltonianCycleTest.java) + * [JohnsonsAlgorithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/JohnsonsAlgorithmTest.java) * [KosarajuTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/KosarajuTest.java) * [TarjansAlgorithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/TarjansAlgorithmTest.java) * [WelshPowellTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/WelshPowellTest.java) @@ -904,6 +914,7 @@ * [EulersFunctionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/EulersFunctionTest.java) * [FactorialRecursionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FactorialRecursionTest.java) * [FactorialTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FactorialTest.java) + * [FastExponentiationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FastExponentiationTest.java) * [FastInverseSqrtTests](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FastInverseSqrtTests.java) * [FFTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FFTTest.java) * [FibonacciJavaStreamsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FibonacciJavaStreamsTest.java) @@ -1116,6 +1127,7 @@ * [NextGreaterElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/NextGreaterElementTest.java) * [NextSmallerElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/NextSmallerElementTest.java) * [PostfixToInfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PostfixToInfixTest.java) + * [PrefixEvaluatorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java) * [PrefixToInfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PrefixToInfixTest.java) * [SortStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/SortStackTest.java) * [StackPostfixNotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/StackPostfixNotationTest.java) From 90a5561924c38393c11f987b054e72a3565dc1e4 Mon Sep 17 00:00:00 2001 From: Hardik Pawar Date: Sun, 13 Oct 2024 12:24:10 +0530 Subject: [PATCH 3/4] Fix --- .../java/com/thealgorithms/stacks/PrefixEvaluatorTest.java | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java b/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java index af52e0f17ee8..e2faa61955b3 100644 --- a/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java +++ b/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java @@ -3,9 +3,8 @@ import static org.junit.jupiter.api.Assertions.assertEquals; import static org.junit.jupiter.api.Assertions.assertThrows; -import org.junit.jupiter.api.Test; - import java.util.EmptyStackException; +import org.junit.jupiter.api.Test; public class PrefixEvaluatorTest { From 6f50206c2d3c5430edf4a2743a63af1fb76ba816 Mon Sep 17 00:00:00 2001 From: Hardik Pawar Date: Sun, 13 Oct 2024 12:32:02 +0530 Subject: [PATCH 4/4] Fix --- .../java/com/thealgorithms/stacks/PrefixEvaluator.java | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java b/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java index 98143b843083..eb2ce95e18d8 100644 --- a/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java +++ b/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java @@ -1,5 +1,6 @@ package com.thealgorithms.stacks; +import java.util.Set; import java.util.Stack; /** @@ -14,6 +15,8 @@ public final class PrefixEvaluator { private PrefixEvaluator() { } + private static final Set OPERATORS = Set.of("+", "-", "*", "/"); + /** * Evaluates the given prefix expression and returns the result. * @@ -32,7 +35,7 @@ public static int evaluatePrefix(String expression) { int operand2 = stack.pop(); stack.push(applyOperator(token, operand1, operand2)); } else { - stack.push(Integer.parseInt(token)); + stack.push(Integer.valueOf(token)); } } @@ -50,7 +53,7 @@ public static int evaluatePrefix(String expression) { * @return true if the token is an operator, false otherwise. */ private static boolean isOperator(String token) { - return token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/"); + return OPERATORS.contains(token); } /**