Merge branch 'master' into jeeva/isogram

Author: JeevaRamanathan

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

@@ -0,0 +1,63 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Implementation to count number of bits to be flipped to convert A to B
+ *
+ * Problem: Given two numbers A and B, count the number of bits needed to be
+ * flipped to convert A to B.
+ *
+ * Example:
+ * A = 10 (01010 in binary)
+ * B = 20 (10100 in binary)
+ * XOR = 30 (11110 in binary) - positions where bits differ
+ * Answer: 4 bits need to be flipped
+ *
+ * Time Complexity: O(log n) - where n is the number of set bits
+ * Space Complexity: O(1)
+ *
+ *@author [Yash Rajput](https://github.com/the-yash-rajput)
+ */
+public final class CountBitsFlip {
+
+    private CountBitsFlip() {
+        throw new AssertionError("No instances.");
+    }
+
+    /**
+     * Counts the number of bits that need to be flipped to convert a to b
+     *
+     * Algorithm:
+     * 1. XOR a and b to get positions where bits differ
+     * 2. Count the number of set bits in the XOR result
+     * 3. Use Brian Kernighan's algorithm: n & (n-1) removes rightmost set bit
+     *
+     * @param a the source number
+     * @param b the target number
+     * @return the number of bits to flip to convert A to B
+     */
+    public static long countBitsFlip(long a, long b) {
+        int count = 0;
+
+        // XOR gives us positions where bits differ
+        long xorResult = a ^ b;
+
+        // Count set bits using Brian Kernighan's algorithm
+        while (xorResult != 0) {
+            xorResult = xorResult & (xorResult - 1); // Remove rightmost set bit
+            count++;
+        }
+
+        return count;
+    }
+
+    /**
+     * Alternative implementation using Long.bitCount().
+     *
+     * @param a the source number
+     * @param b the target number
+     * @return the number of bits to flip to convert a to b
+     */
+    public static long countBitsFlipAlternative(long a, long b) {
+        return Long.bitCount(a ^ b);
+    }
+}

src/main/java/com/thealgorithms/conversions/TimeConverter.java

@@ -0,0 +1,97 @@
+package com.thealgorithms.conversions;
+
+import java.util.Locale;
+import java.util.Map;
+
+/**
+ * A utility class to convert between different units of time.
+ *
+ * <p>This class supports conversions between the following units:
+ * <ul>
+ *   <li>seconds</li>
+ *   <li>minutes</li>
+ *   <li>hours</li>
+ *   <li>days</li>
+ *   <li>weeks</li>
+ *   <li>months (approximated as 30.44 days)</li>
+ *   <li>years (approximated as 365.25 days)</li>
+ * </ul>
+ *
+ * <p>The conversion is based on predefined constants in seconds.
+ * Results are rounded to three decimal places for consistency.
+ *
+ * <p>This class is final and cannot be instantiated.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Unit_of_time">Wikipedia: Unit of time</a>
+ */
+public final class TimeConverter {
+
+    private TimeConverter() {
+        // Prevent instantiation
+    }
+
+    /**
+     * Supported time units with their equivalent in seconds.
+     */
+    private enum TimeUnit {
+        SECONDS(1.0),
+        MINUTES(60.0),
+        HOURS(3600.0),
+        DAYS(86400.0),
+        WEEKS(604800.0),
+        MONTHS(2629800.0), // 30.44 days
+        YEARS(31557600.0); // 365.25 days
+
+        private final double seconds;
+
+        TimeUnit(double seconds) {
+            this.seconds = seconds;
+        }
+
+        public double toSeconds(double value) {
+            return value * seconds;
+        }
+
+        public double fromSeconds(double secondsValue) {
+            return secondsValue / seconds;
+        }
+    }
+
+    private static final Map<String, TimeUnit> UNIT_LOOKUP
+        = Map.ofEntries(Map.entry("seconds", TimeUnit.SECONDS), Map.entry("minutes", TimeUnit.MINUTES), Map.entry("hours", TimeUnit.HOURS), Map.entry("days", TimeUnit.DAYS), Map.entry("weeks", TimeUnit.WEEKS), Map.entry("months", TimeUnit.MONTHS), Map.entry("years", TimeUnit.YEARS));
+
+    /**
+     * Converts a time value from one unit to another.
+     *
+     * @param timeValue the numeric value of time to convert; must be non-negative
+     * @param unitFrom the unit of the input value (e.g., "minutes", "hours")
+     * @param unitTo the unit to convert into (e.g., "seconds", "days")
+     * @return the converted value in the target unit, rounded to three decimals
+     * @throws IllegalArgumentException if {@code timeValue} is negative
+     * @throws IllegalArgumentException if either {@code unitFrom} or {@code unitTo} is not supported
+     */
+    public static double convertTime(double timeValue, String unitFrom, String unitTo) {
+        if (timeValue < 0) {
+            throw new IllegalArgumentException("timeValue must be a non-negative number.");
+        }
+
+        TimeUnit from = resolveUnit(unitFrom);
+        TimeUnit to = resolveUnit(unitTo);
+
+        double secondsValue = from.toSeconds(timeValue);
+        double converted = to.fromSeconds(secondsValue);
+
+        return Math.round(converted * 1000.0) / 1000.0;
+    }
+
+    private static TimeUnit resolveUnit(String unit) {
+        if (unit == null) {
+            throw new IllegalArgumentException("Unit cannot be null.");
+        }
+        TimeUnit resolved = UNIT_LOOKUP.get(unit.toLowerCase(Locale.ROOT));
+        if (resolved == null) {
+            throw new IllegalArgumentException("Invalid unit '" + unit + "'. Supported units are: " + UNIT_LOOKUP.keySet());
+        }
+        return resolved;
+    }
+}

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

@@ -0,0 +1,94 @@
+package com.thealgorithms.bitmanipulation;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Random;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for CountBitsFlip.
+ * Covers:
+ *  - simple examples
+ *  - zeros and identical values
+ *  - negative numbers and two's complement edge cases
+ *  - Long.MIN_VALUE / Long.MAX_VALUE
+ *  - randomized consistency checks between two implementations
+ */
+@DisplayName("CountBitsFlip Tests")
+class CountBitsFlipTest {
+
+    @Test
+    @DisplayName("Example: A=10, B=20 => 4 bits")
+    void exampleTenTwenty() {
+        long a = 10L;
+        long b = 20L;
+        long expected = 4L;
+        assertEquals(expected, CountBitsFlip.countBitsFlip(a, b), "Brian Kernighan implementation should return 4");
+        assertEquals(expected, CountBitsFlip.countBitsFlipAlternative(a, b), "Long.bitCount implementation should return 4");
+    }
+
+    @Test
+    @DisplayName("Identical values => 0 bits")
+    void identicalValues() {
+        long a = 123456789L;
+        long b = 123456789L;
+        long expected = 0L;
+        assertEquals(expected, CountBitsFlip.countBitsFlip(a, b));
+        assertEquals(expected, CountBitsFlip.countBitsFlipAlternative(a, b));
+    }
+
+    @Test
+    @DisplayName("Both zeros => 0 bits")
+    void bothZeros() {
+        assertEquals(0L, CountBitsFlip.countBitsFlip(0L, 0L));
+        assertEquals(0L, CountBitsFlip.countBitsFlipAlternative(0L, 0L));
+    }
+
+    @Test
+    @DisplayName("Small example: A=15 (1111), B=8 (1000) => 3 bits")
+    void smallExample() {
+        long a = 15L; // 1111
+        long b = 8L; // 1000
+        long expected = 3L; // differs in three low bits
+        assertEquals(expected, CountBitsFlip.countBitsFlip(a, b));
+        assertEquals(expected, CountBitsFlip.countBitsFlipAlternative(a, b));
+    }
+
+    @Test
+    @DisplayName("Negative values: -1 vs 0 => 64 bits (two's complement all ones)")
+    void negativeVsZero() {
+        long a = -1L;
+        long b = 0L;
+        long expected = 64L; // all 64 bits differ
+        assertEquals(expected, CountBitsFlip.countBitsFlip(a, b));
+        assertEquals(expected, CountBitsFlip.countBitsFlipAlternative(a, b));
+    }
+
+    @Test
+    @DisplayName("Long.MIN_VALUE vs Long.MAX_VALUE => 64 bits")
+    void minMaxLongs() {
+        long a = Long.MIN_VALUE;
+        long b = Long.MAX_VALUE;
+        long expected = 64L; // MAX ^ MIN yields all ones on 64-bit long
+        assertEquals(expected, CountBitsFlip.countBitsFlip(a, b));
+        assertEquals(expected, CountBitsFlip.countBitsFlipAlternative(a, b));
+    }
+
+    @Test
+    @DisplayName("Randomized consistency: both implementations agree across many pairs")
+    void randomizedConsistency() {
+        final int iterations = 1000;
+        final Random rnd = new Random(12345L); // deterministic seed for reproducibility
+
+        for (int i = 0; i < iterations; i++) {
+            long a = rnd.nextLong();
+            long b = rnd.nextLong();
+
+            long res1 = CountBitsFlip.countBitsFlip(a, b);
+            long res2 = CountBitsFlip.countBitsFlipAlternative(a, b);
+
+            assertEquals(res2, res1, () -> String.format("Mismatch for a=%d, b=%d: impl1=%d, impl2=%d", a, b, res1, res2));
+        }
+    }
+}

src/test/java/com/thealgorithms/conversions/TimeConverterTest.java

@@ -0,0 +1,69 @@
+package com.thealgorithms.conversions;
+
+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.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.MethodSource;
+
+class TimeConverterTest {
+
+    @ParameterizedTest(name = "{0} {1} -> {2} {3}")
+    @CsvSource({"60, seconds, minutes, 1", "120, seconds, minutes, 2", "2, minutes, seconds, 120", "2, hours, minutes, 120", "1, days, hours, 24", "1, weeks, days, 7", "1, months, days, 30.438", "1, years, days, 365.25", "3600, seconds, hours, 1", "86400, seconds, days, 1",
+        "604800, seconds, weeks, 1", "31557600, seconds, years, 1"})
+    void
+    testValidConversions(double value, String from, String to, double expected) {
+        assertEquals(expected, TimeConverter.convertTime(value, from, to));
+    }
+
+    @Test
+    @DisplayName("Zero conversion returns zero")
+    void testZeroValue() {
+        assertEquals(0.0, TimeConverter.convertTime(0, "seconds", "hours"));
+    }
+
+    @Test
+    @DisplayName("Same-unit conversion returns original value")
+    void testSameUnitConversion() {
+        assertEquals(123.456, TimeConverter.convertTime(123.456, "minutes", "minutes"));
+    }
+
+    @Test
+    @DisplayName("Negative value throws exception")
+    void testNegativeValue() {
+        assertThrows(IllegalArgumentException.class, () -> TimeConverter.convertTime(-5, "seconds", "minutes"));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"lightyears, seconds", "minutes, centuries"})
+    void testInvalidUnits(String from, String to) {
+        assertThrows(IllegalArgumentException.class, () -> TimeConverter.convertTime(10, from, to));
+    }
+
+    @Test
+    @DisplayName("Null unit throws exception")
+    void testNullUnit() {
+        assertThrows(IllegalArgumentException.class, () -> TimeConverter.convertTime(10, null, "seconds"));
+
+        assertThrows(IllegalArgumentException.class, () -> TimeConverter.convertTime(10, "minutes", null));
+
+        assertThrows(IllegalArgumentException.class, () -> TimeConverter.convertTime(10, null, null));
+    }
+
+    static Stream<org.junit.jupiter.params.provider.Arguments> roundTripCases() {
+        return Stream.of(org.junit.jupiter.params.provider.Arguments.of(1.0, "hours", "minutes"), org.junit.jupiter.params.provider.Arguments.of(2.5, "days", "hours"), org.junit.jupiter.params.provider.Arguments.of(1000, "seconds", "minutes"));
+    }
+
+    @ParameterizedTest
+    @MethodSource("roundTripCases")
+    @DisplayName("Round-trip conversion returns original value")
+    void testRoundTripConversion(double value, String from, String to) {
+        double converted = TimeConverter.convertTime(value, from, to);
+        double roundTrip = TimeConverter.convertTime(converted, to, from);
+        assertEquals(Math.round(value * 1000.0) / 1000.0, Math.round(roundTrip * 1000.0) / 1000.0, 0.05);
+    }
+}