【leetcode】大数相加

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