大数相加

Given two numbers represented as strings, return sum of the numbers as a string.

string addStr(const string& num1, const string& num2){int i = num1.size()-1;int j = num2.size()-1;string ans = "";int ad = 0;while (i >= 0 && j >= 0){int cur = num1[i] - '0' + num2[j] - '0' + ad;char c = cur % 10 + '0';ad = cur / 10;ans += c;--i;--j;}while (i >= 0){int cur = num1[i] - '0' + ad;char c = cur % 10 + '0';ad = cur / 10;ans += c;--i;}while (j >= 0){int cur = num2[j] - '0' + ad;char c = cur % 10 + '0';ad = cur / 10;ans += c;--j;}if (ad > 0){char c = ad + '0';ans += c;}return string(ans.rbegin(), ans.rend());}