diff --git a/DIRECTORY.md b/DIRECTORY.md index 3e210b57788e..4fb916996aac 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -268,6 +268,7 @@ * greedyalgorithms * [ActivitySelection](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/ActivitySelection.java) * [CoinChange](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java) + * [DigitSeparation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/DigitSeparation.java) * [FractionalKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/FractionalKnapsack.java) * [GaleShapley](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/GaleShapley.java) * [JobSequencing](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/JobSequencing.java) @@ -545,6 +546,7 @@ * [DecimalToAnyUsingStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DecimalToAnyUsingStack.java) * [DuplicateBrackets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DuplicateBrackets.java) * [InfixToPostfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/InfixToPostfix.java) + * [InfixToPrefix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/InfixToPrefix.java) * [LargestRectangle](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/LargestRectangle.java) * [MaximumMinimumWindow](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/MaximumMinimumWindow.java) * [NextGreaterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextGreaterElement.java) @@ -759,6 +761,7 @@ * greedyalgorithms * [ActivitySelectionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/ActivitySelectionTest.java) * [CoinChangeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/CoinChangeTest.java) + * [DigitSeparationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/DigitSeparationTest.java) * [FractionalKnapsackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/FractionalKnapsackTest.java) * [GaleShapleyTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/GaleShapleyTest.java) * [JobSequencingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/JobSequencingTest.java) @@ -976,6 +979,7 @@ * [DecimalToAnyUsingStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/DecimalToAnyUsingStackTest.java) * [DuplicateBracketsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/DuplicateBracketsTest.java) * [InfixToPostfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/InfixToPostfixTest.java) + * [InfixToPrefixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/InfixToPrefixTest.java) * [LargestRectangleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/LargestRectangleTest.java) * [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) diff --git a/src/main/java/com/thealgorithms/stacks/InfixToPrefix.java b/src/main/java/com/thealgorithms/stacks/InfixToPrefix.java new file mode 100644 index 000000000000..3d90d14e0d1e --- /dev/null +++ b/src/main/java/com/thealgorithms/stacks/InfixToPrefix.java @@ -0,0 +1,92 @@ +package com.thealgorithms.stacks; + +import java.util.Stack; +import java.util.regex.Matcher; +import java.util.regex.Pattern; + +public final class InfixToPrefix { + private InfixToPrefix() { + } + + /** + * Convert an infix expression to a prefix expression using stack. + * + * @param infixExpression the infix expression to convert + * @return the prefix expression + * @throws IllegalArgumentException if the infix expression has unbalanced brackets + * @throws NullPointerException if the infix expression is null + */ + public static String infix2Prefix(String infixExpression) throws IllegalArgumentException { + if (infixExpression == null) { + throw new NullPointerException("Input expression cannot be null."); + } + infixExpression = infixExpression.trim(); + if (infixExpression.isEmpty()) { + return ""; + } + if (!BalancedBrackets.isBalanced(filterBrackets(infixExpression))) { + throw new IllegalArgumentException("Invalid expression: unbalanced brackets."); + } + + StringBuilder output = new StringBuilder(); + Stack stack = new Stack<>(); + // Reverse the infix expression for prefix conversion + String reversedInfix = new StringBuilder(infixExpression).reverse().toString(); + for (char element : reversedInfix.toCharArray()) { + if (Character.isLetterOrDigit(element)) { + output.append(element); + } else if (element == ')') { + stack.push(element); + } else if (element == '(') { + while (!stack.isEmpty() && stack.peek() != ')') { + output.append(stack.pop()); + } + stack.pop(); + } else { + while (!stack.isEmpty() && precedence(element) < precedence(stack.peek())) { + output.append(stack.pop()); + } + stack.push(element); + } + } + while (!stack.isEmpty()) { + output.append(stack.pop()); + } + + // Reverse the result to get the prefix expression + return output.reverse().toString(); + } + + /** + * Determines the precedence of an operator. + * + * @param operator the operator whose precedence is to be determined + * @return the precedence of the operator + */ + private static int precedence(char operator) { + switch (operator) { + case '+': + case '-': + return 0; + case '*': + case '/': + return 1; + case '^': + return 2; + default: + return -1; + } + } + + /** + * Filters out all characters from the input string except brackets. + * + * @param input the input string to filter + * @return a string containing only brackets from the input string + */ + private static String filterBrackets(String input) { + Pattern pattern = Pattern.compile("[^(){}\\[\\]<>]"); + Matcher matcher = pattern.matcher(input); + return matcher.replaceAll(""); + } +} diff --git a/src/test/java/com/thealgorithms/stacks/InfixToPrefixTest.java b/src/test/java/com/thealgorithms/stacks/InfixToPrefixTest.java new file mode 100644 index 000000000000..91be8a63da62 --- /dev/null +++ b/src/test/java/com/thealgorithms/stacks/InfixToPrefixTest.java @@ -0,0 +1,44 @@ +package com.thealgorithms.stacks; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import java.util.stream.Stream; +import org.junit.jupiter.api.Test; +import org.junit.jupiter.params.ParameterizedTest; +import org.junit.jupiter.params.provider.Arguments; +import org.junit.jupiter.params.provider.MethodSource; + +public class InfixToPrefixTest { + + @ParameterizedTest + @MethodSource("provideValidExpressions") + void testValidExpressions(String infix, String expectedPrefix) throws Exception { + assertEquals(expectedPrefix, InfixToPrefix.infix2Prefix(infix)); + } + + @Test + void testEmptyString() { + // Assuming that an empty string returns an empty prefix or throws an exception + assertEquals("", InfixToPrefix.infix2Prefix("")); + } + + @Test + void testNullValue() { + // Assuming that a null input throws a NullPointerException + assertThrows(NullPointerException.class, () -> InfixToPrefix.infix2Prefix(null)); + } + + private static Stream provideValidExpressions() { + return Stream.of(Arguments.of("3+2", "+32"), // Simple addition + Arguments.of("1+(2+3)", "+1+23"), // Parentheses + Arguments.of("(3+4)*5-6", "-*+3456"), // Nested operations + Arguments.of("a+b*c", "+a*bc"), // Multiplication precedence + Arguments.of("a+b*c/d", "+a/*bcd"), // Division precedence + Arguments.of("a+b*c-d", "-+a*bcd"), // Subtraction precedence + Arguments.of("a+b*c/d-e", "-+a/*bcde"), // Mixed precedence + Arguments.of("a+b*(c-d)", "+a*b-cd"), // Parentheses precedence + Arguments.of("a+b*(c-d)/e", "+a/*b-cde") // Mixed precedence with parentheses + ); + } +}