花花酱 LeetCode 1185. Day of the Week

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:

Solution: LeapYear

Time complexity: O(1)
Space complexity: O(1)

C++

// Author: Huahua

inline bool leapYear(int y) {

return (y % 4 == 0 && y % 100 != 0) || (y % 400 == 0);

}

class Solution {

public:

string dayOfTheWeek(int day, int month, int year) {

vector<string> names = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

vector<int> days = {31, 28 + leapYear(year), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

int sum = 0;

for (int i = 1970; i < year; ++i)

sum += 365 + leapYear(i);

for (int i = 1; i < month; ++i)

sum += days[i - 1];

sum += day;

return names[(sum + 3) % 7];

}

};

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