415. Add Strings

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415. Add Strings

Description

Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and num2 as a string.

You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly.

Example 1:

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Input: num1 = "11", num2 = "123"
Output: "134"

Example 2:

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Input: num1 = "456", num2 = "77"
Output: "533"

Example 3:

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Input: num1 = "0", num2 = "0"
Output: "0"

Constraints:

  • 1 <= num1.length, num2.length <= 10^4
  • num1 and num2 consist of only digits.
  • num1 and num2 don’t have any leading zeros except for the zero itself.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    string addStrings(string num1, string num2) {
        int l1 = num1.size() - 1, l2 = num2.size() - 1, carry = 0;
        string res;
        while (l1 >= 0 || l2 >= 0 || carry) {
            if (l1 >= 0) {
                carry += num1[l1--] - '0';
            }
            if (l2 >= 0) {
                carry += num2[l2--] - '0';
            }
            res.push_back(carry % 10 + '0');
            carry /= 10;
        }
        ranges::reverse(res);
        return res;
    }
};