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Add LowestSetBit (#5567)
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package com.thealgorithms.bitmanipulation;
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/**
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* Lowest Set Bit
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* @author Prayas Kumar (https://github.com/prayas7102)
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*/
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public final class LowestSetBit {
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// Private constructor to hide the default public one
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private LowestSetBit() {
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}
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/**
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* Isolates the lowest set bit of the given number. For example, if n = 18
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* (binary: 10010), the result will be 2 (binary: 00010).
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*
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* @param n the number whose lowest set bit will be isolated
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* @return the isolated lowest set bit of n
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*/
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public static int isolateLowestSetBit(int n) {
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// Isolate the lowest set bit using n & -n
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return n & -n;
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}
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/**
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* Clears the lowest set bit of the given number.
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* For example, if n = 18 (binary: 10010), the result will be 16 (binary: 10000).
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*
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* @param n the number whose lowest set bit will be cleared
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* @return the number after clearing its lowest set bit
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*/
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public static int clearLowestSetBit(int n) {
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// Clear the lowest set bit using n & (n - 1)
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return n & (n - 1);
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}
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}
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package com.thealgorithms.bitmanipulation;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import org.junit.jupiter.api.Test;
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/**
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* Test case for Lowest Set Bit
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* @author Prayas Kumar (https://github.com/prayas7102)
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*/
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public class LowestSetBitTest {
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@Test
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void testLowestSetBitWithPositiveNumber() {
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// Test with a general positive number
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assertEquals(2, LowestSetBit.isolateLowestSetBit(18)); // 18 in binary: 10010, lowest bit is 2
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}
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@Test
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void testLowestSetBitWithZero() {
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// Test with zero (edge case, no set bits)
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assertEquals(0, LowestSetBit.isolateLowestSetBit(0)); // 0 has no set bits, result should be 0
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}
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@Test
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void testLowestSetBitWithOne() {
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// Test with number 1 (lowest set bit is 1 itself)
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assertEquals(1, LowestSetBit.isolateLowestSetBit(1)); // 1 in binary: 0001, lowest bit is 1
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}
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@Test
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void testLowestSetBitWithPowerOfTwo() {
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// Test with a power of two (only one set bit)
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assertEquals(16, LowestSetBit.isolateLowestSetBit(16)); // 16 in binary: 10000, lowest bit is 16
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}
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@Test
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void testLowestSetBitWithAllBitsSet() {
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// Test with a number with multiple set bits (like 7)
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assertEquals(1, LowestSetBit.isolateLowestSetBit(7)); // 7 in binary: 111, lowest bit is 1
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}
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@Test
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void testLowestSetBitWithNegativeNumber() {
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// Test with a negative number (-1 in two's complement has all bits set)
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assertEquals(1, LowestSetBit.isolateLowestSetBit(-1)); // -1 in two's complement is all 1s, lowest bit is 1
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}
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@Test
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void testLowestSetBitWithLargeNumber() {
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// Test with a large number
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assertEquals(64, LowestSetBit.isolateLowestSetBit(448)); // 448 in binary: 111000000, lowest bit is 64
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}
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@Test
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void testClearLowestSetBitFor18() {
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// n = 18 (binary: 10010), expected result = 16 (binary: 10000)
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assertEquals(16, LowestSetBit.clearLowestSetBit(18));
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}
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@Test
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void testClearLowestSetBitFor10() {
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// n = 10 (binary: 1010), expected result = 8 (binary: 1000)
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assertEquals(8, LowestSetBit.clearLowestSetBit(10));
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}
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@Test
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void testClearLowestSetBitFor7() {
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// n = 7 (binary: 0111), expected result = 6 (binary: 0110)
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assertEquals(6, LowestSetBit.clearLowestSetBit(7));
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}
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@Test
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void testClearLowestSetBitFor0() {
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// n = 0 (binary: 0000), no set bits to clear, expected result = 0
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assertEquals(0, LowestSetBit.clearLowestSetBit(0));
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}
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@Test
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void testClearLowestSetBitForNegativeNumber() {
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// Test negative number to see how it behaves with two's complement
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// n = -1 (binary: all 1s in two's complement), expected result = -2 (clearing lowest set bit)
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assertEquals(-2, LowestSetBit.clearLowestSetBit(-1));
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}
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}
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