(Leetcode)504. Base 7

Given an integer, return its base 7 string representation.

Example 1:
Input: 100
Output: "202"
Example 2:
Input: -7
Output: "-10"

Solution:

public class Solution {
    public String convertToBase7(int num) {
        StringBuilder sb = new StringBuilder();
        boolean flag = true;    // 标记num 符号
        if (num == 0){
            return "0";
        }
        if(num < 0) {
            flag = false;
        }

        while (num != 0) {
            sb.append(Math.abs(num) % 7);
            num = num / 7;
        }
        if (!flag) {
            return "-" + sb.reverse().toString();
        }
        return sb.reverse().toString();
    }
}