LeetCode [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.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

class Solution { public: string addStrings(string num1, string num2) { int i = num1.size()-1, j = num2.size()-1; string ret = ""; int c = 0; while(i>=0 && j>=0){ int s = (num1[i--]-'0') + (num2[j--]-'0') + c; ret = to_string(s%10) + ret; c = s/10; } while(i>=0){ int s = (num1[i--]-'0') + c; ret = to_string(s%10) + ret; c = s/10; } while(j>=0){ int s = (num2[j--]-'0') + c; ret = to_string(s%10) + ret; c = s/10; } if(c) ret = to_string(c) + ret; return ret; } };