## Description

LeetCode Problem 415.

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:

``````1
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Input: num1 = "11", num2 = "123"
Output: "134"
``````

Example 2:

``````1
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Input: num1 = "456", num2 = "77"
Output: "533"
``````

Example 3:

``````1
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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.

## Sample C++ Code

``````1
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class Solution {
public:
string addStrings(string num1, string num2) {
int len1 = num1.size();
int len2 = num2.size();
int len = max(len1, len2);
int c = 0;
int s = 0;
string sum;

for (int i = 0; i < len; i ++) {
s = c;
if (i < len1)
s += num1[len1 - i - 1] - '0';
if (i < len2)
s += num2[len2 - i - 1] - '0';
c = s / 10;
s = s % 10;
sum += to_string(s);
}

if (c != 0)
sum += to_string(c);

reverse(sum.begin(), sum.end());

return sum;
}
};
``````