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Problem19.js
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Problem19.js
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/*
* Prompt: How many Sundays fell on the first of the month during the twentieth century?
*
* Execute: node Problem19.js
*
* Answer: 171
*
* Notes: Brute force answer. 6ms execution
*/
var current = {
weekday: 0, // 0 = Monday, 6 = Sunday
day: 1,
month: 1,
year: 1900,
monthlength: 999
};
count = 0;
while (true) {
if (current.day == 1) {
// Calculate days in month
if (current.month == 2) {
current.monthlength = 28;
if (current.year % 4 == 0) { // Leap year?
if (current.year % 100 == 0) {
if (current.year % 400 == 0) {
current.monthlength = 29;
}
} else {
current.monthlength = 29;
}
}
} else if ([4, 6, 9, 11].indexOf(current.month) >= 0) { // 30 day
current.monthlength = 30;
} else { // 31 days
current.monthlength = 31;
}
}
current.day += 1;
if (current.day > current.monthlength) {
current.day = 1;
current.month += 1;
if (current.month > 12) {
current.month = 1;
current.year += 1;
if (current.year > 2000) {
break;
}
}
}
current.weekday += 1;
if (current.weekday > 6) {
current.weekday = 0; // Wrap to Monday
}
if (current.year != 1900) { // Not part of the 20th century
if (current.day == 1 && current.weekday == 6) {
count += 1;
}
}
}
console.log(count);