Number of Days Between Two Dates
<p>Write a program to count the number of days between two dates.</p>

<p>The two dates are given as strings, their format is <code>YYYY-MM-DD</code>&nbsp;as shown in the examples.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> date1 = "2019-06-29", date2 = "2019-06-30"
<strong>Output:</strong> 1
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> date1 = "2020-01-15", date2 = "2019-12-31"
<strong>Output:</strong> 15
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The given dates are valid&nbsp;dates between the years <code>1971</code> and <code>2100</code>.</li>
</ul>
Math; String
class Solution:
    def daysBetweenDates(self, date1: str, date2: str) -> int:
        def isLeapYear(year: int) -> bool:
            return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)

        def daysInMonth(year: int, month: int) -> int:
            days = [
                31,
                28 + int(isLeapYear(year)),
                31,
                30,
                31,
                30,
                31,
                31,
                30,
                31,
                30,
                31,
            ]
            return days[month - 1]

        def calcDays(date: str) -> int:
            year, month, day = map(int, date.split("-"))
            days = 0
            for y in range(1971, year):
                days += 365 + int(isLeapYear(y))
            for m in range(1, month):
                days += daysInMonth(year, m)
            days += day
            return days

        return abs(calcDays(date1) - calcDays(date2))
