Base 7

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].

Solution:

class Solution {
    public String convertToBase7(int num) {
        if (num < 0) return "-" + convertToBase7(-num);
        if (num == 0) return "0";
        StringBuilder sb = new StringBuilder();
        while (num > 0) {
            sb.append(num % 7);
            num = num / 7;
        }
        return sb.reverse().toString();
    }
}