504. Base 7

题目：

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].

链接：https://leetcode.com/problems/base-7/#/description

3/30/2017

17ms

1. 要注意负数

2. 第11行int到char转化

3. 题中负数到正数不会溢出，但是如果去掉范围条件呢？

 1 public class Solution {
 2     public String convertToBase7(int num) {
 3         StringBuilder sb = new StringBuilder();
 4         StringBuilder r = new StringBuilder();
 5         if (num == 0) return "0";
 6         if (num < 0) {
 7             r.append('-');
 8             num = -num;
 9         }
10         while (num != 0) {
11             sb.append((char)(num % 7 + '0'));
12             num /= 7;
13         }
14         
15         return r.append(sb.reverse()).toString();
16     }
17 }