题解-不设定数组

#include<bits/stdc++.h>
using namespace std;
string add(string s1, string s2) {

string s = "";
int i = s1.size() - 1, j = s2.size() - 1, x = 0;
while (i >= 0 || j >= 0 || x > 0) {
    int n1 = (i >= 0) ? s1[i] - '0' : 0;
    int n2 = (j >= 0) ? s2[i] - '0' : 0;
	int sum = n1 + n2 + x;
	x = sum / 10;
	sum %= 10;
    s = char(sum + '0') + s;
    i--, j--;
}
while (s[0] == '0') s.erase(0, 1);
return s;

}
int main() {

string s1, s2;
cin >> s1 >> s2;
cout << add(s1, s2);
return 0;

}