415. Add Strings | Leetcode solution

 415. 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.

solution:

class Solution {

public:

    string addStrings(string num1, string num2) {

            string  result = "";

        //   string num = "";

        // sum = num + sum;

        int l1 = num1.length();

        int l2 = num2.length();

        if(l1 > l2)

        {

              string t(l1-l2 ,'0' );

              num2 = t + num2;

              l2 = l1;

        }

        else

        if(l2 > l1)

        {

              string t(l2-l1 ,'0' );

              num1 = t + num1;

              l1 = l2 ;

        }

        int carry = 0;

        for(int i = l1 -1 ; i >= 0 ; i--)

        {

            int a = num1[i] -48;

            int b = num2[i] - 48;

            int sum_num = a+b+carry;

            if(sum_num /10 == 0 && sum_num != 10)

            {

                carry = 0;

                char h =sum_num+48;

                result = h + result ;

            }

            else

            {

                 carry = 1;

                  int y = sum_num %10;

                char h = y + 48;

                result = h+ result ;

            }

            

                

        } 

         if(carry == 1)

         {

             result = "1"+result;

         }

        return result;

        

    }

};