LeetCode Base 7

原题链接在这里：https://leetcode.com/problems/base-7/#/description

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].

题解：

每次num%7放在前面. num再除以7. 最后加上正负号.

注意corner case: num = 0.

Time Complexity: O(num/7). Space: O(1).

AC Java:

 public class Solution {
     public String convertToBase7(int num) {
         if(num == 0){
             return "0";
         }

         boolean isNeg = false;
         if(num < 0){
             isNeg = true;
         }

         num = Math.abs(num);
         StringBuilder sb = new StringBuilder();
         while(num != 0){
             sb.insert(0, num%7);
             num /= 7;
         }

         return isNeg ? "-"+sb.toString() : sb.toString();
     }
 }