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## Problem

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

Example 1:

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


Example 2:

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


Example 3:

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


Constraints:

1 <= num1.length, num2.length <= 104 num1 and num2 consist of only digits. num1 and num2 don’t have any leading zeros except for the zero itself.

## Code

class Solution {
public String addStrings(String num1, String num2) {
int len1 = num1.length();
int len2 = num2.length();

String str1 = new StringBuilder(num1).reverse().toString();
String str2 = new StringBuilder(num2).reverse().toString();

int carry = 0;
StringBuilder res = new StringBuilder();

for(int i = 0; i < Math.max(len1, len2); i++){
int x = i >= len1 ? 0 : (str1.charAt(i) - '0');
int y = i >= len2 ? 0 : (str2.charAt(i) - '0');
int sum = x + y + carry;

res.append(String.valueOf(sum % 10));
carry = sum / 10;
}

if(carry != 0){
res.append(String.valueOf(carry));
}

return res.reverse().toString();
}
}