504. Base 7

Given an integer, return its base 7 string representation.

Example 1:

Input: 100
Output: "202"

Example 2:

Input: -7
Output: "-10"

10进制转成7进制

C++（3ms）：

class Solution {
public:
    string convertToBase7(int num) {
        int x = abs(num) ;
        string str ;
        do
        {
          str = to_string(x%7) + str ;
        } while (x/=7);
        return num>=0?str:"-"+str;
    }
};

Java（15ms）：

public class Solution {
    public String convertToBase7(int num) {
        return Integer.toString(num, 7) ;
    }
}

把一个6进制的数转成7进制

public String convertToBase7(int num) {
    return Integer.toString(Integer.parseInt(num+"", 6), 7) ;
}