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Head of Career Skills Development & Coaching

*Based on past data of successful IK students

Given two binary strings `a`

and `b`

, add them and return the resultant binary string.

```
{
"a": "10",
"b": "01"
}
```

Output:

```
"11"
```

```
{
"a": "110",
"b": "111"
}
```

Output:

```
"1101"
```

Return the binary string that is formed by adding two input strings.

The input string may contain leading zeroes, but the output string should not.

Do not directly convert input strings to integers. Solve this problem without using any built-in library for handling large numbers.

Constraints:

- 1 <= Length of the input strings <= 10
^{5} - All the characters of the input strings will be either
`0`

or`1`

.

```
/*
Asymptotic complexity in terms of the total length of input strings \`n\`:
* Time: O(n).
* Auxiliary space: O(n).
* Total space: O(n).
*/
string add_strings(string &a, string &b) {
// Variables pointing to the last character of the strings.
int i = a.size() - 1, j = b.size() - 1;
// Variable to track the carry at each step.
int carry = 0;
// Answer string.
string answer = "";
// Looping over the string.
while (i >= 0 || j >= 0) {
// x and y are the current digits.
int x = (i >= 0) ? (a[i--] - '0') : 0;
int y = (j >= 0) ? (b[j--] - '0') : 0;
// currentSum stores Sum of the current digits with previous carry.
int currentSum = x + y + carry;
// Updating answer and carry.
answer = to_string(currentSum % 2) + answer;
carry = currentSum / 2;
}
// If there is carry remain then adding 1 to the left of the answer string.
if (carry > 0) {
answer = to_string(1) + answer;
}
// Removing leading zeros.
reverse(answer.begin(), answer.end());
while (answer.size() > 1 and answer.back() == '0') {
answer.pop_back();
}
reverse(answer.begin(), answer.end());
// Returning the answer.
return answer;
}
```

We hope that these solutions to the Add binary Strings Problem have helped you level up your coding skills. You can expect problems like these at top tech companies like Amazon and Google.

If you are preparing for a tech interview at FAANG or any other Tier-1 tech company, register for Interview Kickstart’s FREE webinar to understand the best way to prepare.

Interview Kickstart offers interview preparation courses taught by FAANG+ tech leads and seasoned hiring managers. Our programs include a comprehensive curriculum, unmatched teaching methods, and career coaching to help you nail your next tech interview.

We offer 18 interview preparation courses, each tailored to a specific engineering domain or role, including the most in-demand and highest-paying domains and roles, such as:

- Back-end Engineering Interview Course
- Front-end Engineering Interview Course
- Full Stack Developer Interview Course

To learn more, register for the FREE webinar.

Note: Input and Output will already be taken care of.

Given two binary strings `a`

and `b`

, add them and return the resultant binary string.

```
{
"a": "10",
"b": "01"
}
```

Output:

```
"11"
```

```
{
"a": "110",
"b": "111"
}
```

Output:

```
"1101"
```

Return the binary string that is formed by adding two input strings.

The input string may contain leading zeroes, but the output string should not.

Do not directly convert input strings to integers. Solve this problem without using any built-in library for handling large numbers.

Constraints:

- 1 <= Length of the input strings <= 10
^{5} - All the characters of the input strings will be either
`0`

or`1`

.

```
/*
Asymptotic complexity in terms of the total length of input strings \`n\`:
* Time: O(n).
* Auxiliary space: O(n).
* Total space: O(n).
*/
string add_strings(string &a, string &b) {
// Variables pointing to the last character of the strings.
int i = a.size() - 1, j = b.size() - 1;
// Variable to track the carry at each step.
int carry = 0;
// Answer string.
string answer = "";
// Looping over the string.
while (i >= 0 || j >= 0) {
// x and y are the current digits.
int x = (i >= 0) ? (a[i--] - '0') : 0;
int y = (j >= 0) ? (b[j--] - '0') : 0;
// currentSum stores Sum of the current digits with previous carry.
int currentSum = x + y + carry;
// Updating answer and carry.
answer = to_string(currentSum % 2) + answer;
carry = currentSum / 2;
}
// If there is carry remain then adding 1 to the left of the answer string.
if (carry > 0) {
answer = to_string(1) + answer;
}
// Removing leading zeros.
reverse(answer.begin(), answer.end());
while (answer.size() > 1 and answer.back() == '0') {
answer.pop_back();
}
reverse(answer.begin(), answer.end());
// Returning the answer.
return answer;
}
```

We hope that these solutions to the Add binary Strings Problem have helped you level up your coding skills. You can expect problems like these at top tech companies like Amazon and Google.

- Back-end Engineering Interview Course
- Front-end Engineering Interview Course
- Full Stack Developer Interview Course

To learn more, register for the FREE webinar.

**Attend our free webinar to amp up your career and get the salary you deserve.**

Hosted By

Ryan Valles

Founder, Interview Kickstart