class Solution {
public:
string convertToBase7(int num) {
if(num == 0) return "0";
string result;
bool is_minus = num < 0;
num = abs(num);
while(num) {
result = to_string(num % 7) + result;
num /= 7;
}
if(is_minus) result = '-' + result;
return result;
}
};