504. Base 7

Given an integer, return its base 7 string representation.

Example 1:

Input: 100Output: "202"

Example 2:

Input: -7Output: "-10"

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

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