415. Add Strings

• Difficulty: Easy

• Topics: String

• Similar Questions:

  • Add Two Numbers

  • Multiply Strings

  • Add to Array-Form of Integer

Problem:

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

Note:

Solutions:

class Solution {
public:
    string addStrings(string num1, string num2) {
        string ret;
        int carry = 0;
        int i1 = num1.length() - 1;
        int i2 = num2.length() - 1; 

        while (carry != 0 || i1 >= 0 && i2 >= 0) {
            int value = carry + (i1 >= 0 ? num1[i1--] - '0': 0) + (i2 >= 0 ? num2[i2--] - '0' : 0);
            ret.push_back(value % 10 + '0');
            carry = value / 10;
        }

        reverse(ret.begin(), ret.end());

        if (i1 >= 0) {
            ret = num1.substr(0, i1 + 1) + ret;
        }

        if (i2 >= 0) {
            ret = num2.substr(0, i2 + 1) + ret;
        }

        return ret;

    }
};