[Swift]LeetCode1185. 一周中的第几天 | Day of the Week

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Given a date, return the corresponding day of the week for that date.

The input is given as three integers representing the day, month and year respectively.

Return the answer as one of the following values {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}.

Example 1:

Input: day = 31, month = 8, year = 2019
Output: "Saturday"

Example 2:

Input: day = 18, month = 7, year = 1999
Output: "Sunday"

Example 3:

Input: day = 15, month = 8, year = 1993
Output: "Sunday"

Constraints:

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

---

给你一个日期，请你设计一个算法来判断它是对应一周中的哪一天。

输入为三个整数：day、month 和 year，分别表示日、月、年。

您返回的结果必须是这几个值中的一个 {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}。

示例 1：

输入：day = 31, month = 8, year = 2019
输出："Saturday"

示例 2：

输入：day = 18, month = 7, year = 1999
输出："Sunday"

示例 3：

输入：day = 15, month = 8, year = 1993
输出："Sunday"

提示：

• 给出的日期一定是在 1971 到 2100 年之间的有效日期。

---

Runtime: 0 ms

Memory Usage: 20.5 MB

class Solution {
    let S:[String] = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
    func dayOfTheWeek(_ day: Int, _ month: Int, _ year: Int) -> String {
        var month = month
        var year = year
        if month < 3
        {
            year -= 1
            month += 12
        }
        let w:Int = (year + year / 4 - year / 100 + year / 400 + (13 * month + 8) / 5 + day) % 7
        return S[w]
    }
}

---

0ms

class Solution {
    func dayOfTheWeek(_ day: Int, _ month: Int, _ year: Int) -> String {
        let months = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
        let days = ["Friday", "Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday"]
        var res = 0
        for y in stride(from: 1972, to: year, by: 4) {
            res += 1
        }
        if year % 4 == 0 && year != 2100 && month > 2 {
            res += 1
        }
        res += (year - 1971) * 365
        for m in 1..<month {
            res += months[m - 1]
        }
        res += (day - 1)
        res %= 7
        return days[res]
    }
}

---

4ms

class Solution {
    func dayOfTheWeek(_ day: Int, _ month: Int, _ year: Int) -> String {
        guard day >= 1 && day <= 31 && month >= 1 && month <= 12 && year >= 1971 && year <= 2100 else {
            return ""
        }
        
        func isLeapYear(_ year: Int) -> Bool {
            return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)
        }
        
        // 1971-1-1 => Friday
        let weekName = ["Friday", "Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday"]
        // Days to 01-01, leadYear
        let monthDays = [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335]
        var days = 0
     
        for y in 1971 ..< year {
            days += (isLeapYear(y) ? 366 : 365)
        }
        
        if month < 3 {
            days += monthDays[month - 1] + day - 1
        }
        else {
            days += (monthDays[month - 1] + (isLeapYear(year) ? 0 : -1) + day - 1)
        }
        
        return weekName[days % 7]
    }
}

---

8ms

class Solution {
    func dayOfTheWeek(_ day: Int, _ month: Int, _ year: Int) -> String {
        let formatter  = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"
        let date = formatter.date(from: "(year)-(month)-(day)")
        let myCalendar = Calendar(identifier: .gregorian)
        let weekDay = myCalendar.component(.weekday, from: date!)
        
        return ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"][weekDay - 1]
    }
}