415. Add Strings

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

Note:

1. The length of both num1 and num2 is < 5100.
2. Both num1 and num2 contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

class Solution {public:    string addStrings(string s1, string s2) {        if(s1.length()==0) return s2;if(s2.length()==0) return s1;reverse(s1.begin(),s1.end());reverse(s2.begin(),s2.end());string result="";int i=0,count=0;int max_length=s1.length()>s2.length()?s1.length():s2.length();while(i<max_length){char a=i>=s1.length()?'0':s1[i];char b=i>=s2.length()?'0':s2[i];int sum=a-'0'+b-'0'+count;count=sum/10;char c=sum%10+48;result.push_back(c);i++;}if(count!=0)  result.push_back((char)(count+48));reverse(result.begin(),result.end());return result;    }};