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19.js
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19.js
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/*
You are given the following information, but you may prefer to do some research for yourself.
1 Jan 1900 was a Monday.
Thirty days has September,
April, June and November.
All the rest have thirty-one,
Saving February alone,
Which has twenty-eight, rain or shine.
And on leap years, twenty-nine.
A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
*/
var findSundays = function() {
var sundays = 0,
totalDaysPassed = 0,
leapYear, daysInMonth;
var days = {
1: 31,
2: 28,
3: 31,
4: 30,
5: 31,
6: 30,
7: 31,
8: 31,
9: 30,
10: 31,
11: 30,
12: 31
};
for (var year = 1900; year <= 2000; year++) {
leapYear = year % 4 === 0;
if (leapYear && (year % 100 === 0) && !(year % 400 === 0)) leapYear = false;
for (var month = 1; month <= 12; month++) {
daysInMonth = days[month];
if (month === 2 && leapYear) daysInMonth++;
totalDaysPassed += daysInMonth;
if ((totalDaysPassed + 1) % 7 === 0 && year > 1900) sundays++;
}
}
return sundays;
}
console.log(findSundays())