LeetCode 504. Base 7

题目描述：

Given an integer, return its base 7 string representation.

Example 1:

Input: 100
Output: "202"

Example 2:

Input: -7
Output: "-10"

Note: The input will be in range of [-1e7, 1e7].

使用除法来进行进制转换。

class Solution {
public:
    string convertToBase7(int num) {
        int sign = num >= 0 ? 1 : -1;
        string ans;
        num = abs(num);
        if (num == 0) return string("0");
        while (num > 0) {
            ans.insert(ans.begin(), (num % 7) + '0');
            num /= 7;
        }
        if (sign > 0) return ans;
        else return string("-") + ans;
    }
};