67. Add Binary

Given two binary strings a and b, return their sum as a binary string.

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Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

Constraints:

1 <= a.length, b.length <= 104
a and b consist only of ‘0’ or ‘1’ characters.
Each string does not contain leading zeros except for the zero itself.

Solution

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class Solution {
   public String addBinary(String a, String b) {
        int i = a.length() - 1;
        int j = b.length() - 1;
        
        int carry = 0;
        StringBuilder sb = new StringBuilder();
        while (i >= 0 || j >= 0) {
            
            int c1 = (i >= 0) ? a.charAt(i) - '0': 0;
            int c2 = (j >= 0) ? b.charAt(j) - '0': 0;
            
            int c3 = c1 + c2 + carry;
            
            if (carry > 0) {
                carry = 0;
            }
            if (c3 == 3) {
                carry = 1;
                sb.insert(0, '1');
            } else if (c3 == 2) {
                carry = 1;
                sb.insert(0, '0');
            } else if (c3 == 1) {
                sb.insert(0, '1');
            } else {
                sb.insert(0, '0');
            }
            i--;
            j--;
        }
       
        if (carry > 0) {
             sb.insert(0, '1');
        }
       return sb.toString();
    }
    public String addBinary2(String a, String b) {
        Integer i1 = Integer.parseInt(a, 2);
        Integer i2 = Integer.parseInt(b, 2);
        
        return Integer.toBinaryString(i1 + i2);
    }
}

Solution#

Solution