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.
public class Solution {
public int DaysBetweenDates(string date1, string date2) {
return Math.Abs(countSince1971(date1) - countSince1971(date2));
}
public int countSince1971(String date) {
var monthDays = new int[]{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
var data = date.Split('-');
int year = int.Parse(data[0]);
int month = int.Parse(data[1]);
int day = int.Parse(data[2]);
for (int i = 1971; i < year; i++) {
day += isALeapYear(i) ? 366 : 365;
}
for (int i = 1; i < month; i++) {
if (isALeapYear(year) && i == 2) {
day += 1;
}
day += monthDays[i];
}
return day;
}
public bool isALeapYear(int year) {
return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}
}Time Complexity: O(n)
Space Complexity: O(1)
