Bit Manipulation: 67. Add Binary

Author: shaikrasheed99

README.md

@@ -53,6 +53,7 @@
   * [260](https://leetcode.com/problems/single-number-iii/). Single Number III - [code](src/bit_manipulation/easy/TwoSingleNumbers.java)
   * [405](https://leetcode.com/problems/convert-a-number-to-hexadecimal/). Convert a Number to Hexadecimal - [code](src/bit_manipulation/easy/ConvertANumberToHexadecimal.java)
   * [268](https://leetcode.com/problems/missing-number/). Missing Number - [code](src/bit_manipulation/easy/MissingNumber.java)
+  * [67](https://leetcode.com/problems/add-binary/). Add Binary - [code](src/bit_manipulation/easy/AddBinary.java)
   * [Gfg](https://practice.geeksforgeeks.org/problems/check-whether-k-th-bit-is-set-or-not-1587115620/1). Check whether K-th bit is set or not - [code](src/bit_manipulation/easy/CheckKthBitIsSet.java)
   * [Gfg](https://practice.geeksforgeeks.org/problems/odd-or-even3618/1). Odd or Even - [code](src/bit_manipulation/easy/OddOrEven.java)
   * [Gfg](https://practice.geeksforgeeks.org/problems/set-kth-bit3724/1). Set kth bit - [code](src/bit_manipulation/easy/SetKthBit.java)

src/bit_manipulation/easy/AddBinary.java

@@ -0,0 +1,128 @@
+package bit_manipulation.easy;
+
+/***
+ * Problem 67 in Leetcode: https://leetcode.com/problems/add-binary/
+ *
+ * Given two binary strings a and b, return their sum as a binary string.
+ *
+ * Example 1:
+ * Input: a = "1001010101011010101010110101111", b = "1010010101001010101010"
+ * Output: "1001010110101101010100001011001"
+ *
+ * Example 2:
+ * Input: a = "1010", b = "1011"
+ * Output: "10101"
+ */
+
+public class AddBinary {
+    public static void main(String[] args) {
+        String a = "1001010101011010101010110101111", b = "1010010101001010101010";
+
+        System.out.println("Brute Force: " + addBinaryBruteForce(a, b));
+        System.out.println("Optimized: " + addBinaryOptimized(a, b));
+    }
+
+    private static String addBinaryBruteForce(String a, String b) {
+        int n = a.length() - 1;
+        int m = b.length() - 1;
+        char carry = '0';
+        StringBuilder sb = new StringBuilder();
+
+        while ((n >= 0) && (m >= 0)) {
+            char bit1 = a.charAt(n);
+            char bit2 = b.charAt(m);
+
+            if ((bit1 == '1') && (bit2 == '1')) {
+                if (carry == '1') {
+                    sb.append('1');
+                } else {
+                    sb.append('0');
+                    carry = '1';
+                }
+            } else if ((bit1 == '0') && (bit2 == '0')) {
+                if (carry == '1') {
+                    sb.append('1');
+                    carry = '0';
+                } else {
+                    sb.append('0');
+                }
+            } else {
+                if (carry == '1') {
+                    sb.append('0');
+                } else {
+                    sb.append('1');
+                }
+            }
+            n--;
+            m--;
+        }
+
+        while (n >= 0) {
+            char bit = a.charAt(n);
+            if (carry == '1') {
+                if (bit == '1') {
+                    sb.append('0');
+                } else {
+                    sb.append('1');
+                    carry = '0';
+                }
+            } else {
+                sb.append(bit);
+            }
+            n--;
+        }
+
+        while (m >= 0) {
+            char bit = b.charAt(m);
+            if (carry == '1') {
+                if (bit == '1') {
+                    sb.append('0');
+                } else {
+                    sb.append('1');
+                    carry = '0';
+                }
+            } else {
+                sb.append(bit);
+            }
+            m--;
+        }
+
+        if (carry == '1') {
+            sb.append('1');
+        }
+
+        return sb.reverse().toString();
+    }
+
+    private static String addBinaryOptimized(String a, String b) {
+        int n = a.length() - 1;
+        int m = b.length() - 1;
+        int carry = 0;
+        StringBuilder sb = new StringBuilder();
+
+        while ((n >= 0) || (m >= 0)) {
+            int sum = 0;
+            if ((n >= 0) && (a.charAt(n) == '1')) {
+                sum++;
+            }
+            if ((m >= 0) && (b.charAt(m) == '1')) {
+                sum++;
+            }
+            sum += carry;
+            if (sum >= 2) {
+                carry = 1;
+            } else {
+                carry = 0;
+            }
+            sb.append(sum % 2);
+            n--;
+            m--;
+        }
+
+        if (carry == 1) {
+            sb.append('1');
+        }
+
+        return sb.reverse().toString();
+    }
+}