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1360. Number of Days Between Two Dates 👎

  • Time: $O(1)$
  • Space: $O(1)$
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class Solution {
 public:
  int daysBetweenDates(string date1, string date2) {
    return abs(daysFrom1971(date1) - daysFrom1971(date2));
  }

 private:
  const vector<int> days{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

  int daysFrom1971(const string& date) {
    const int year = stoi(date1.substr(0, 4));
    const int month = stoi(date1.substr(5, 2));
    const int day = stoi(date1.substr(8, 2));
    int res = 0;
    for (int i = 1971; i < year; ++i)
      res += isLeapYear(i) ? 366 : 365;
    for (int i = 0; i < month; ++i)
      res += days[i];
    if (month > 2 && isLeapYear(year))
      ++res;
    res += day;
    return res;
  }

  bool isLeapYear(int year) {
    return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
  };
};

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class Solution {
  public int daysBetweenDates(String date1, String date2) {
    return Math.abs(daysFrom1971(date1) - daysFrom1971(date2));
  }

  private static final int[] days = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

  private int daysFrom1971(final String date) {
    final int year = Integer.valueOf(date.substring(0, 4));
    final int month = Integer.valueOf(date.substring(5, 7));
    final int day = Integer.valueOf(date.substring(8));
    int res = 0;
    for (int i = 1971; i < year; ++i)
      res += isLeapYear(i) ? 366 : 365;
    for (int i = 0; i < month; ++i)
      res += days[i];
    if (month > 2 && isLeapYear(year))
      ++res;
    return res + day;
  }

  private boolean isLeapYear(int year) {
    return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
  };
}

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class Solution:
  def daysBetweenDates(self, date1: str, date2: str) -> int:
    days = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

    def isLeapYear(year: int) -> bool:
      return year % 4 == 0 and year % 100 != 0 or year % 400 == 0

    def daysFrom1971(date: str) -> int:
      year, month, day = map(int, date.split('-'))
      return 365 * (year - 1971) + sum(map(isLeapYear, range(1971, year))) + \
          sum(days[:month]) + day + (month > 2 and isLeapYear(year))

    return abs(daysFrom1971(date1) - daysFrom1971(date2))