leetcode504: 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 String convertToBase7(int num) {int f = Math.abs(num);StringBuffer str = new StringBuffer();ArrayList list = new ArrayList();while (f / 7 != 0) {list.add(f % 7);f = f / 7;}list.add(f % 7);for (int i = list.size() - 1; i >= 0; i--)str.append(list.get(i));String result;if (num < 0)result = "-" + str.toString();elseresult = str.toString();return result;}