# Solution to Project Euler Problem 19: Counting Sundays - 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)?

**Updated:**Oct. 19, 2021 —

**Training Time:**2 minutes

Overseen by: Archangel Macsika

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**Topic:**Project Euler Problem 19: Counting Sundays

**Difficulty:** Easy.

**Objective:** 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)?

**Input:** None.

**Expected Output:** 171.

### Sikademy Solution in Java Programming Language

```
package sikademy;
/**
*
* @author Archangel Macsika
* Copyright (c) Sikademy. All rights reserved
*/
public class SikademyEulerSolution {
public String run() {
int count = 0;
for (int y = 1901; y <= 2000; y++) {
for (int m = 1; m <= 12; m++) {
if (dayOfWeek(y, m, 1) == 0) // Sunday
count++;
}
}
return Integer.toString(count);
}
// Return value: 0 = Sunday, 1 = Monday, ..., 6 = Saturday.
private static int dayOfWeek(int year, int month, int day) {
if (year < 0 || year > 10000 || month < 1 || month > 12 || day < 1 || day > 31)
throw new IllegalArgumentException();
// Zeller's congruence algorithm
int m = (month - 3 + 4800) % 4800;
int y = (year + m / 12) % 400;
m %= 12;
return (y + y/4 - y/100 + (13 * m + 2) / 5 + day + 2) % 7;
}
public static void main(String[] args) {
SikademyEulerSolution solution = new SikademyEulerSolution();
System.out.println(solution.run());
}
}
```

### Sikademy Solution in Python Programming Language

```
#
# @author Archangel Macsika
# Copyright (c) Sikademy. All rights reserved.
#
import datetime
def compute():
ans = sum(1
for y in range(1901, 2001)
for m in range(1, 13)
if datetime.date(y, m, 1).weekday() == 6)
return str(ans)
if __name__ == "__main__":
print(compute())
```