题目如下：

Write a program to count the number of days between two dates.

The two dates are given as strings, their format is YYYY-MM-DD as shown in the examples.

Example 1:

Input: date1 = "2019-06-29", date2 = "2019-06-30"
Output: 1

Example 2:

Input: date1 = "2020-01-15", date2 = "2019-12-31"
Output: 15

Constraints:

• The given dates are valid dates between the years 1971 and 2100.

解题思路：我直接用的python的库求解的。

代码如下：

class Solution(object):
    def daysBetweenDates(self, date1, date2):
        """
        :type date1: str
        :type date2: str
        :rtype: int
        """
        import datetime
        d1 = datetime.datetime.strptime(date1, '%Y-%m-%d')
        d2 = datetime.datetime.strptime(date2, '%Y-%m-%d')
        return abs((d1 - d2).days)