class Solution {
public:
string reformatNumber(string number) {
string ans;
number.erase(remove(number.begin(), number.end(), '-'), number.end());
number.erase(remove(number.begin(), number.end(), ' '), number.end());
int i = 0; // number's index
for (i = 0; i + 4 < number.length(); i += 3)
ans += number.substr(i, 3) + '-';
const int countFinalDigits = number.length() - i;
if (countFinalDigits < 4)
ans += number.substr(i);
else // countFinalDigits == 4
ans += number.substr(i, 2) + '-' + number.substr(i + 2);
return ans;
}
};