AddStrings-LCQ.cpp

/*
Add Strings

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:

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.
*/

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