大数相加

[guodongxiaren]

考虑最简单的情况，只有正整数的情况。

[guodongxiaren]

// Example program
#include <iostream>
#include <string>
#include <algorithm>
#include <sstream>

using namespace std;

string add(const string& A, const string& B) {
    string a(A);
    string b(B);
    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());

    int ia = 0, ib = 0;
    int la = a.size(), lb = b.size();

    int t = 0;
    stringstream ss;
    while (ia < la || ib < lb) {

        if (ia < la) {
            t += a[ia++] - '0';
        }
        if (ib < lb) {
            t += b[ib++] - '0';
        }
        ss<<t%10;
        t /= 10;
    }
    // t == 1
    if (t > 0) {
        ss<<t;
    }
    string s = ss.str();
    reverse(s.begin(), s.end());
    return s;
}
int main() {
    cout<<add("123", "456")<<endl;
    cout<<add("123", "4567")<<endl;
    cout<<add("4567", "123")<<endl;
}