Merge branch 'master' into SMJI/stack/min_max_const_time

Author: S-M-J-I

DIRECTORY.md

@@ -598,7 +598,9 @@
             * [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)
             * [NextSmallerElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextSmallerElement.java)
+            * [PostfixEvaluator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixEvaluator.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)
@@ -1128,7 +1130,9 @@
             * [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)
+            * [PostfixEvaluatorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PostfixEvaluatorTest.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)

src/main/java/com/thealgorithms/bitmanipulation/BcdConversion.java

@@ -1,56 +1,80 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * This class provides methods to convert between BCD (Binary-Coded Decimal) and binary.
+ * This class provides methods to convert between BCD (Binary-Coded Decimal) and decimal numbers.
  *
- * Binary-Coded Decimal (BCD) is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of binary digits, usually four or eight.
+ * BCD is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of binary digits, usually four or eight.
  *
  * For more information, refer to the
  * <a href="https://en.wikipedia.org/wiki/Binary-coded_decimal">Binary-Coded Decimal</a> Wikipedia page.
  *
  * <b>Example usage:</b>
  * <pre>
- * int binary = BcdConversion.bcdToBinary(0x1234);
- * System.out.println("BCD 0x1234 to binary: " + binary); // Output: 1234
+ * int decimal = BcdConversion.bcdToDecimal(0x1234);
+ * System.out.println("BCD 0x1234 to decimal: " + decimal); // Output: 1234
  *
- * int bcd = BcdConversion.binaryToBcd(1234);
- * System.out.println("Binary 1234 to BCD: " + Integer.toHexString(bcd)); // Output: 0x1234
+ * int bcd = BcdConversion.decimalToBcd(1234);
+ * System.out.println("Decimal 1234 to BCD: " + Integer.toHexString(bcd)); // Output: 0x1234
  * </pre>
  */
 public final class BcdConversion {
     private BcdConversion() {
     }
+
     /**
-     * Converts a BCD (Binary-Coded Decimal) number to binary.
+     * Converts a BCD (Binary-Coded Decimal) number to a decimal number.
+     * <p>Steps:
+     * <p>1. Validate the BCD number to ensure all digits are between 0 and 9.
+     * <p>2. Extract the last 4 bits (one BCD digit) from the BCD number.
+     * <p>3. Multiply the extracted digit by the corresponding power of 10 and add it to the decimal number.
+     * <p>4. Shift the BCD number right by 4 bits to process the next BCD digit.
+     * <p>5. Repeat steps 1-4 until the BCD number is zero.
      *
      * @param bcd The BCD number.
-     * @return The corresponding binary number.
+     * @return The corresponding decimal number.
+     * @throws IllegalArgumentException if the BCD number contains invalid digits.
      */
-    public static int bcdToBinary(int bcd) {
-        int binary = 0;
+    public static int bcdToDecimal(int bcd) {
+        int decimal = 0;
         int multiplier = 1;
+
+        // Validate BCD digits
         while (bcd > 0) {
-            int digit = bcd & 0xF; // Extract the last 4 bits (one BCD digit)
-            binary += digit * multiplier;
+            int digit = bcd & 0xF;
+            if (digit > 9) {
+                throw new IllegalArgumentException("Invalid BCD digit: " + digit);
+            }
+            decimal += digit * multiplier;
             multiplier *= 10;
-            bcd >>= 4; // Shift right by 4 bits to process the next BCD digit
+            bcd >>= 4;
         }
-        return binary;
+        return decimal;
     }
 
     /**
-     * Converts a binary number to BCD (Binary-Coded Decimal).
+     * Converts a decimal number to BCD (Binary-Coded Decimal).
+     * <p>Steps:
+     * <p>1. Check if the decimal number is within the valid range for BCD (0 to 9999).
+     * <p>2. Extract the last decimal digit from the decimal number.
+     * <p>3. Shift the digit to the correct BCD position and add it to the BCD number.
+     * <p>4. Remove the last decimal digit from the decimal number.
+     * <p>5. Repeat steps 2-4 until the decimal number is zero.
      *
-     * @param binary The binary number.
+     * @param decimal The decimal number.
      * @return The corresponding BCD number.
+     * @throws IllegalArgumentException if the decimal number is greater than 9999.
      */
-    public static int binaryToBcd(int binary) {
+    public static int decimalToBcd(int decimal) {
+        if (decimal < 0 || decimal > 9999) {
+            throw new IllegalArgumentException("Value out of bounds for BCD representation: " + decimal);
+        }
+
         int bcd = 0;
         int shift = 0;
-        while (binary > 0) {
-            int digit = binary % 10; // Extract the last decimal digit
-            bcd |= (digit << (shift * 4)); // Shift the digit to the correct BCD position
-            binary /= 10; // Remove the last decimal digit
+        while (decimal > 0) {
+            int digit = decimal % 10;
+            bcd |= (digit << (shift * 4));
+            decimal /= 10;
             shift++;
         }
         return bcd;

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

@@ -0,0 +1,74 @@
+package com.thealgorithms.stacks;
+
+import java.util.Set;
+import java.util.Stack;
+
+/**
+ * Evaluate a postfix (Reverse Polish) expression using a stack.
+ *
+ * <p>Example: Expression "5 6 + 2 *" results in 22.
+ * <p>Applications: Used in calculators and expression evaluation in compilers.
+ *
+ * @author Hardvan
+ */
+public final class PostfixEvaluator {
+    private PostfixEvaluator() {
+    }
+
+    private static final Set<String> OPERATORS = Set.of("+", "-", "*", "/");
+
+    /**
+     * Evaluates the given postfix expression and returns the result.
+     *
+     * @param expression The postfix expression as a string with operands and operators separated by spaces.
+     * @return The result of evaluating the postfix expression.
+     * @throws IllegalArgumentException if the expression is invalid.
+     */
+    public static int evaluatePostfix(String expression) {
+        Stack<Integer> stack = new Stack<>();
+
+        for (String token : expression.split("\\s+")) {
+            if (isOperator(token)) {
+                int operand2 = stack.pop();
+                int operand1 = stack.pop();
+                stack.push(applyOperator(token, operand1, operand2));
+            } else {
+                stack.push(Integer.valueOf(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 OPERATORS.contains(token);
+    }
+
+    /**
+     * 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");
+        };
+    }
+}

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

@@ -0,0 +1,76 @@
+package com.thealgorithms.stacks;
+
+import java.util.Set;
+import java.util.Stack;
+
+/**
+ * Evaluate a prefix (Polish) expression using a stack.
+ *
+ * <p>Example: Expression "+ * 2 3 4" results in 10.
+ * <p>Applications: Useful for implementing compilers and interpreters.
+ *
+ * @author Hardvan
+ */
+public final class PrefixEvaluator {
+    private PrefixEvaluator() {
+    }
+
+    private static final Set<String> OPERATORS = Set.of("+", "-", "*", "/");
+
+    /**
+     * 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<Integer> 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.valueOf(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 OPERATORS.contains(token);
+    }
+
+    /**
+     * 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");
+        };
+    }
+}

src/test/java/com/thealgorithms/bitmanipulation/BcdConversionTest.java

@@ -1,65 +1,85 @@
 package com.thealgorithms.bitmanipulation;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
-/**
- * Unit tests for the BcdConversion class.
- */
 public class BcdConversionTest {
 
-    /**
-     * Test the bcdToBinary method with a BCD number.
-     */
     @Test
-    public void testBcdToBinary() {
-        int binary = BcdConversion.bcdToBinary(0x1234);
-        assertEquals(1234, binary); // BCD 0x1234 should convert to binary 1234
+    public void testBcdToDecimal() {
+        int decimal = BcdConversion.bcdToDecimal(0x1234);
+        assertEquals(1234, decimal); // BCD 0x1234 should convert to decimal 1234
     }
 
-    /**
-     * Test the binaryToBcd method with a binary number.
-     */
     @Test
-    public void testBinaryToBcd() {
-        int bcd = BcdConversion.binaryToBcd(1234);
-        assertEquals(0x1234, bcd); // Binary 1234 should convert to BCD 0x1234
+    public void testDecimalToBcd() {
+        int bcd = BcdConversion.decimalToBcd(1234);
+        assertEquals(0x1234, bcd); // Decimal 1234 should convert to BCD 0x1234
     }
 
-    /**
-     * Test the bcdToBinary method with zero.
-     */
     @Test
-    public void testBcdToBinaryZero() {
-        int binary = BcdConversion.bcdToBinary(0x0);
-        assertEquals(0, binary); // BCD 0x0 should convert to binary 0
+    public void testBcdToDecimalZero() {
+        int decimal = BcdConversion.bcdToDecimal(0x0);
+        assertEquals(0, decimal); // BCD 0x0 should convert to decimal 0
     }
 
-    /**
-     * Test the binaryToBcd method with zero.
-     */
     @Test
-    public void testBinaryToBcdZero() {
-        int bcd = BcdConversion.binaryToBcd(0);
-        assertEquals(0x0, bcd); // Binary 0 should convert to BCD 0x0
+    public void testDecimalToBcdZero() {
+        int bcd = BcdConversion.decimalToBcd(0);
+        assertEquals(0x0, bcd); // Decimal 0 should convert to BCD 0x0
     }
 
-    /**
-     * Test the bcdToBinary method with a single digit BCD number.
-     */
     @Test
-    public void testBcdToBinarySingleDigit() {
-        int binary = BcdConversion.bcdToBinary(0x7);
-        assertEquals(7, binary); // BCD 0x7 should convert to binary 7
+    public void testBcdToDecimalSingleDigit() {
+        int decimal = BcdConversion.bcdToDecimal(0x7);
+        assertEquals(7, decimal); // BCD 0x7 should convert to decimal 7
     }
 
-    /**
-     * Test the binaryToBcd method with a single digit binary number.
-     */
     @Test
-    public void testBinaryToBcdSingleDigit() {
-        int bcd = BcdConversion.binaryToBcd(7);
-        assertEquals(0x7, bcd); // Binary 7 should convert to BCD 0x7
+    public void testDecimalToBcdSingleDigit() {
+        int bcd = BcdConversion.decimalToBcd(7);
+        assertEquals(0x7, bcd); // Decimal 7 should convert to BCD 0x7
+    }
+
+    @Test
+    public void testBcdToDecimalMaxValue() {
+        int decimal = BcdConversion.bcdToDecimal(0x9999);
+        assertEquals(9999, decimal); // BCD 0x9999 should convert to decimal 9999
+    }
+
+    @Test
+    public void testDecimalToBcdMaxValue() {
+        int bcd = BcdConversion.decimalToBcd(9999);
+        assertEquals(0x9999, bcd); // Decimal 9999 should convert to BCD 0x9999
+    }
+
+    @Test
+    public void testBcdToDecimalInvalidHighDigit() {
+        // Testing invalid BCD input where one of the digits is > 9
+        assertThrows(IllegalArgumentException.class, () -> {
+            BcdConversion.bcdToDecimal(0x123A); // Invalid BCD, 'A' is not a valid digit
+        });
+    }
+
+    @Test
+    public void testDecimalToBcdInvalidValue() {
+        // Testing conversion for numbers greater than 9999, which cannot be represented in BCD
+        assertThrows(IllegalArgumentException.class, () -> {
+            BcdConversion.decimalToBcd(10000); // 10000 is too large for BCD representation
+        });
+    }
+
+    @Test
+    public void testBcdToDecimalLeadingZeroes() {
+        int decimal = BcdConversion.bcdToDecimal(0x0234);
+        assertEquals(234, decimal); // BCD 0x0234 should convert to decimal 234, ignoring leading zero
+    }
+
+    @Test
+    public void testDecimalToBcdLeadingZeroes() {
+        int bcd = BcdConversion.decimalToBcd(234);
+        assertEquals(0x0234, bcd); // Decimal 234 should convert to BCD 0x0234
     }
 }