自己餵測資都ok

但是線上測試有後RE有時候OLE

丟submit都RE，求解qq

#include<string>
#include<iostream>
#include<sstream>
using namespace std;

int map(char c)
{
switch(c) {
case 'I':
return 1;
case 'V':
return 5;
case 'X':
return 10;
case 'L':
return 50;
case 'C':
return 100;
case 'D':
return 500;
case 'M':
return 1000;
}
}

int romtoi(string r)
{
int sum = 0, cnt = 0;
for(string::iterator it=r.begin(); it!=r.end(); it++) {
sum += map(*it);
if(map(*(it+1)) > map(*it)) {
sum = map(*(it+1))-sum;
return sum + romtoi(string(it+2, r.end()));
} else if(map(*(it+1)) < map(*it)) {
return sum + romtoi(string(it+1, r.end()));
} else {
cnt++;
}
}
return sum;
}

string _itorom(int i, int base, char c, char d, char e)
{
int k=0, l=0, m=0;
string rt;
while(i/base > 0) {
k++;
if(base>1)
i-=base;
else
i--;
if(k==4){
k=-1;
if(l) m=1;
l=!l;
}
}
if(m) {
rt.push_back(c);
rt.push_back(e);
} else if(l) {
if(k<0) {
rt.push_back(c);
rt.push_back(d);
} else {
rt.push_back(d);
for(int j=0; j<k; j++)
rt.push_back(c);
}
} else {
for(int j=0; j<k; j++)
rt.push_back(c);
}
return rt;
}

string itorom(int i)
{
string r;
if(!i) return "ZERO";
else {
for(int j=0; j<i/1000; j++)
r.push_back('M');
i %= 1000;

r += _itorom(i, 100, 'C', 'D', 'M');
i %= 100;
r += _itorom(i, 10, 'X', 'L', 'C');
i %= 10;
r += _itorom(i, 1, 'I', 'V', 'X');
return r;
}
}

int main()
{
string str;
while(getline(cin, str) && str!="#") {
stringstream ss(str);
string rnum1, rnum2;
int sub=0;

ss >> rnum1 >> rnum2;
sub = romtoi(rnum1) - romtoi(rnum2);
sub = sub>=0? sub: -sub;

cout << itorom(sub) << '\n';
}
}

找到問題了，iterator可能會超過，但我想知道為什麼在我的電腦上跑不會出問題？