Add Binary

                            Solution in C :

char* addBinary(char* a, char* b)
{
    int i, j, k, c = 0;
    char *res;
    
    i = strlen(a);
    j = strlen(b);
    k = i > j ? i : j;
    k += 2;

    res = malloc(k * sizeof(char));
    
    i--;
    j--;
    res[--k] = '\0';
    
    while (--k >= 0) {
        c += i >= 0 ? a[i--] - '0': 0;
        c += j >= 0 ? b[j--] - '0': 0;
        
        res[k] = c % 2 + '0';
        c /= 2;
    }
    
    if (res[0] == '0')
       memmove(res, res + 1, strlen(res) * sizeof(char));
    
    return res;
}
                        

                        Solution in C++ :

class Solution {
 public:
  string addBinary(string a, string b) {
    string ans;
    int carry = 0;
    int i = a.length() - 1;
    int j = b.length() - 1;

    while (i >= 0 || j >= 0 || carry) {
      if (i >= 0)
        carry += a[i--] - '0';
      if (j >= 0)
        carry += b[j--] - '0';
      ans += carry % 2 + '0';
      carry /= 2;
    }

    reverse(begin(ans), end(ans));
    return ans;
  }
};
                    

                        Solution in Java :

class Solution 
{
  public String addBinary(String a, String b) 
  {
    StringBuilder sb = new StringBuilder();
    int carry = 0;
    int i = a.length() - 1;
    int j = b.length() - 1;

    while (i >= 0 || j >= 0 || carry == 1) 
    {
      if(i >= 0)
        carry += a.charAt(i--) - '0';
      if(j >= 0)
        carry += b.charAt(j--) - '0';
      sb.append(carry % 2);
      carry /= 2;
    }
    return sb.reverse().toString();
  }
}
                    

                        Solution in Python : 
                            
class Solution:
  def addBinary(self, a: str, b: str) -> str:
    s = []
    carry = 0
    i = len(a) - 1
    j = len(b) - 1

    while i >= 0 or j >= 0 or carry:
      if i >= 0:
        carry += int(a[i])
        i -= 1
      if j >= 0:
        carry += int(b[j])
        j -= 1
      s.append(str(carry % 2))
      carry //= 2

    return ''.join(reversed(s))