LeetCode 504 - Base 7

https://leetcode.com/problems/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].

https://discuss.leetcode.com/topic/78952/verbose-java-solution

    public String convertTo7(int num) {
        if (num == 0) return "0";
        
        StringBuilder sb = new StringBuilder();
        boolean negative = false;
        
        if (num < 0) {
            negative = true;
        }
        while (num != 0) {
            sb.append(Math.abs(num % 7));
            num = num / 7;
        }
        
        if (negative) {
            sb.append("-");
        }
        
        return sb.reverse().toString();
    }

https://discuss.leetcode.com/topic/78935/java-1-liner-standard-solution

public String convertTo7(int num) {
    return Integer.toString(num, 7);
}

Not using standard library:

    public String convertTo7(int num) {
        if (num == 0) return "0";
        String res = "";
        boolean isNeg = num < 0;
        while (num != 0) {
            res = Math.abs((num % 7)) + res;
            num /= 7;
        }
        return isNeg ? "-" + res : res;
    }

http://blog.csdn.net/zhouziyu2011/article/details/55004517
取余数加入到result的前面，除以7，直到小于7，最后再把num加入result的前面。
注意负数。

1. 
       public String convertTo7(int num) {  
2.         String result = "";  
3.         int flag = 0;  
4.         if (num < 0) {  
5.             flag = 1;  
6.             num = Math.abs(num);  
7.         }  
8.         while(num >= 7) {  
9.             result = num % 7 + result;  
10.             num = num / 7;  
11.         }  
12.         result = num + result;  
13.         if (flag == 1)  
14.             result = "-" + result;  
15.         return result;  
16.     }