【leetcode】1556. Thousand Separator

题目如下：

Given an integer n, add a dot (".") as the thousands separator and return it in string format.

Example 1:

Input: n = 987
Output: "987"

Example 2:

Input: n = 1234
Output: "1.234"

Example 3:

Input: n = 123456789
Output: "123.456.789"

Example 4:

Input: n = 0
Output: "0"

Constraints:

• 0 <= n < 2^31

解题思路：很简单的题目，倒序处理，每三位加一个'.'即可。

代码如下：

class Solution(object):
    def thousandSeparator(self, n):
        """
        :type n: int
        :rtype: str
        """
        res = ''
        sn = str(n)[::-1]
        for i in range(len(sn)):
            if i > 0 and i % 3 == 0:
                res = sn[i] + '.' + res
            else:res = sn[i] + res
        return res