Leetcode Note: Go - Day of the Week

var months = map[int]int{
    0: 0,
    1: 31,
    2: 59,
    3: 90,
    4: 120,
    5: 151,
    6: 181,
    7: 212,
    8: 243,
    9: 273,
    10: 304,
    11: 334,
}

var weekDays = map[int]string{
    0: "Monday",
    1: "Tuesday",
    2: "Wednesday",
    3: "Thursday",
    4: "Friday",
    5: "Saturday",
    6: "Sunday",
}

// 1st January 0001 - Saturday
var firstDay = 5

func dayOfTheWeek(day int, month int, year int) string {
    checkLeapYear := year
    // do not inlude this year
    // if we don't pass February 
    if month <= 2 {
        checkLeapYear -= 1
    }
    
    leapYears := (checkLeapYear / 4) - (checkLeapYear / 100) + (checkLeapYear / 400)
    
    
    monthDays := months[month-1]
    
	// we count years from 1st not from 0th
    days := 365 * (year-1) 
	days += monthDays 
	days += day
	days += leapYears
	days += 1
    
    return weekDays[(days+firstDay) % 7]
}