Add Strings Problem Statement

Return sum of two given integers a and b in the string format.

Example

{
"a": "10",
"b": "20"
}

Output:

"30"

10 + 20 = 30, hence the output string will be “30”

Notes

• The input string can have trailing zeros, but the output string should not have the trailing zeros.
• We expect you to solve this problem without using any built-in library for handling large numbers.

Constraints:

• 1 <= length of both the strings <= 10⁵
• a and b consist of only digits

Code For Add Strings Solution: Naive

/*
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_two_strings(string &a, string &b) {
    string answer;

    int i = a.size() - 1, j = b.size() - 1, carry = 0;

    // Loop till both the strings or carry is not processed.
    while (i >= 0 || j >= 0 || carry) {
        // Store the sum of the current digits(if exists) of both the strings with carry from the previous
        // stage.
        int currentSum = (i >= 0 ? a[i--] - '0' : 0) + (j >= 0 ? b[j--] - '0' : 0) + carry;

        answer.push_back((currentSum % 10) + '0');
        carry = currentSum / 10;
    }

    // Remove trailing zeros.
    while (answer.size() > 1 and answer.back() == '0') {
        answer.pop_back();
    }

    reverse(answer.begin(), answer.end());
    return answer;
}

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

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