# 67. Add Binary

### Description

Given two binary strings, return their sum (also a binary string).

The input strings are both **non-empty** and contains only characters `1` or `0`.

### Constraints

* Each string consists only of `'0'` or `'1'` characters.
* `1 <= a.length, b.length <= 10^4`
* Each string is either `"0"` or doesn't contain any leading zero.

### **Approach**

### Links

* [GeeksforGeeks](https://www.geeksforgeeks.org/program-to-add-two-binary-strings)
* [Leetcode](https://leetcode.com/problems/add-binary)
* ProgramCreek

### Examples

{% tabs %}
{% tab title="Example 1" %}
**Input:** a = "11", b = "1"&#x20;

**Output:** "100"
{% endtab %}

{% tab title="Example 2" %}
**Input:** a = "1010", b = "1011"

**Output:** "10101"
{% endtab %}
{% endtabs %}

### Solutions

{% tabs %}
{% tab title="Solution 1" %}

```java
/**
 * 
 * 
 */

class Solution {
    public String addBinary(String a, String b) {
        int alen = a.length();
        int blen = b.length();
        int sum = 0;
        StringBuilder result = new StringBuilder("");
        while(alen > 0 || blen > 0) {
            if(alen > 0 && a.charAt(--alen) == '1') {
                sum++;
            }
            if(blen > 0 && b.charAt(--blen) == '1') {
                sum++;
            }
            result.insert(0, (sum%2));
            sum /= 2;
        }
        if(sum == 1) {
            result.insert(0, "1");
        }
        return result.toString();
    }
}
```

{% endtab %}

{% tab title="Solution 2" %}

```java
/**
 * 
 * 
 */

class Solution {
    public String addBinary(String a, String b) {
        int alen = a.length();
        int blen = b.length();
        int sum = 0;
        StringBuilder result = new StringBuilder("");
        while(alen > 0 || blen > 0) {
            sum += (alen > 0)? a.charAt(--alen)-'0': 0;
            sum += (blen > 0)? b.charAt(--blen)-'0': 0;
            result.append(sum&1);
            sum /= 2;
        }
        if(sum == 1) {
            result.append(1);
        }
        return result.reverse().toString();
    }
}
```

{% endtab %}
{% endtabs %}

### **Follow up**

*


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