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）：

 1 class Solution {
 2 public:
 3     string convertToBase7(int num) {
 4         int x = abs(num) ;
 5         string str ;
 6         do
 7         {
 8           str = to_string(x%7) + str ;
 9         } while (x/=7);
10         return num>=0?str:"-"+str;
11     }
12 };

Java（15ms）：

1 public class Solution {
2     public String convertToBase7(int num) {
3         return Integer.toString(num, 7) ;
4     }
5 }

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) ;
}