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Add binary addition (TheAlgorithms#5593)
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‎DIRECTORY.md

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* [GrahamScan](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/geometry/GrahamScan.java)
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* greedyalgorithms
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* [ActivitySelection](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/ActivitySelection.java)
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* [BinaryAddition](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/BinaryAddition.java)
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* [CoinChange](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java)
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* [DigitSeparation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/DigitSeparation.java)
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* [FractionalKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/FractionalKnapsack.java)
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* [GrahamScanTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/geometry/GrahamScanTest.java)
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* greedyalgorithms
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* [ActivitySelectionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/ActivitySelectionTest.java)
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* [BinaryAdditionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/BinaryAdditionTest.java)
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* [CoinChangeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/CoinChangeTest.java)
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* [DigitSeparationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/DigitSeparationTest.java)
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* [FractionalKnapsackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/FractionalKnapsackTest.java)

‎src/main/java/com/thealgorithms/greedyalgorithms/BinaryAddition.java

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package com.thealgorithms.greedyalgorithms;
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import java.util.Collections;
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/**
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* BinaryAddition class to perform binary addition of two binary strings.
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*/
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public class BinaryAddition {
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/**
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* Computes the sum of two binary characters and a carry.
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* @param a First binary character ('0' or '1').
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* @param b Second binary character ('0' or '1').
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* @param carry The carry from the previous operation ('0' or '1').
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* @return The sum as a binary character ('0' or '1').
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*/
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public char sum(char a, char b, char carry) {
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int count = 0;
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if (a == '1') {
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count++;
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}
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if (b == '1') {
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count++;
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}
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if (carry == '1') {
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count++;
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}
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return count % 2 == 0 ? '0' : '1';
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}
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/**
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* Computes the carry for the next higher bit from two binary characters and a carry.
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* @param a First binary character ('0' or '1').
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* @param b Second binary character ('0' or '1').
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* @param carry The carry from the previous operation ('0' or '1').
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* @return The carry for the next bit ('0' or '1').
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*/
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public char carry(char a, char b, char carry) {
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int count = 0;
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if (a == '1') {
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count++;
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}
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if (b == '1') {
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count++;
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}
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if (carry == '1') {
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count++;
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}
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return count >= 2 ? '1' : '0';
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}
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/**
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* Adds two binary strings and returns their sum as a binary string.
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* @param a First binary string.
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* @param b Second binary string.
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* @return Binary string representing the sum of the two binary inputs.
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*/
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public String addBinary(String a, String b) {
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// Padding the shorter string with leading zeros
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int maxLength = Math.max(a.length(), b.length());
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a = String.join("", Collections.nCopies(maxLength - a.length(), "0")) + a;
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b = String.join("", Collections.nCopies(maxLength - b.length(), "0")) + b;
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StringBuilder result = new StringBuilder();
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char carry = '0';
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// Iterating over the binary strings from the least significant to the most significant bit
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for (int i = maxLength - 1; i >= 0; i--) {
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char sum = sum(a.charAt(i), b.charAt(i), carry);
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carry = carry(a.charAt(i), b.charAt(i), carry);
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result.append(sum);
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}
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// If there's a remaining carry, append it
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if (carry == '1') {
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result.append('1');
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}
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// Reverse the result as we constructed it from the least significant bit
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return result.reverse().toString();
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}
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}

‎src/test/java/com/thealgorithms/greedyalgorithms/BinaryAdditionTest.java

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package com.thealgorithms.greedyalgorithms;
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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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public class BinaryAdditionTest {
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BinaryAddition binaryAddition = new BinaryAddition();
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@Test
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public void testEqualLengthNoCarry() {
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String a = "1010";
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String b = "1101";
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String expected = "10111";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testEqualLengthWithCarry() {
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String a = "1111";
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String b = "1111";
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String expected = "11110";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testDifferentLengths() {
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String a = "101";
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String b = "11";
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String expected = "1000";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testAllZeros() {
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String a = "0";
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String b = "0";
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String expected = "0";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testAllOnes() {
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String a = "1111";
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String b = "1111";
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String expected = "11110";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testOneZeroString() {
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String a = "0";
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String b = "10101";
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String expected = "10101";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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// Test the other way around
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a = "10101";
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b = "0";
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expected = "10101";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testLargeBinaryNumbers() {
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String a = "101010101010101010101010101010";
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String b = "110110110110110110110110110110";
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String expected = "1100001100001100001100001100000";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testOneMuchLonger() {
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String a = "1";
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String b = "11111111";
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String expected = "100000000";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testEmptyStrings() {
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String a = "";
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String b = "";
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String expected = ""; // Adding two empty strings should return 0
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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@Test
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public void testAlternatingBits() {
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String a = "10101010";
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String b = "01010101";
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String expected = "11111111";
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assertEquals(expected, binaryAddition.addBinary(a, b));
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}
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}

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