Java: How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

GeoTeo :

I am new to programming and java and I am trying to solve the following problem: How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

Here is my code:

int count, sum = 0;           
for (int i = 1901; i < 2001; i++) {
    LocalDate test = LocalDate.of(i, 1, 1);
    sum += test.lengthOfYear();
}
for (int i = 1; i < sum; i++) {
    LocalDate date1 = LocalDate.of(1901, 1, 1);
    date1 = date1.plusDays(i);
    if (date1.getMonth() == JANUARY && date1.getDayOfWeek() == SUNDAY) {
        count++;
    }
}
System.out.println(count);

If I print the results, it seems to be working fine.

My result is 443, but the correct answer is 171. What am I doing wrong?

Thank you!

David Pérez Cabrera :

I see some mistakes:

public static void main(String[] args) {
    int count, sum = 0;           
    for (int i = 1901; i < 2001; i++) { // There is a mistake here, I dont know what you want to compute in this loop!
        LocalDate test = LocalDate.of(i,1,1);
        sum += test.lengthOfYear();
    }
    for (int i = 1; i < sum; i++) {
        LocalDate date1 = LocalDate.of(1901,1,1); // There is a mistake here, date1 must be outside of this loop
        date1 = date1.plusDays(i); // There is a mistake here, plusDays why?? 
    if(date1.getMonth() == JANUARY && date1.getDayOfWeek() == SUNDAY) { // There is a mistake here, why are you cheking this: date1.getMonth() == JANUARY ?
        count++;
        }
    }
    System.out.println(count);
}

A simple solution:

public static void main(String[] args) {
    int count = 0;
    LocalDate date1 = LocalDate.of(1901, Month.JANUARY, 1);
    LocalDate endDate = LocalDate.of(2001, Month.JANUARY, 1);
    while (date1.isBefore(endDate)) {
        date1 = date1.plusMonths(1);
        if (date1.getDayOfWeek() == DayOfWeek.SUNDAY) {
            count++;
        }
    }
    System.out.println(count);
}

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