504. Base 7

static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();

class Solution 
{
public:
    string convertToBase7(int num) 
    {
        if(num==0)
            return "0";
        string res;
        int k=abs(num);
        int remain=0;
        while(k)
        {
            remain=k%7;
            res.push_back(remain+'0');
            k/=7;
        }
        if(num<0)
            res.push_back('-');
        reverse(res.begin(),res.end());
        return res;
    }
};

 转7进制，余除，问题不大