## Project Euler – Problem 19

Problem 19: How many Sundays fell on the first of the month during the twentieth century?

``` public class Main{ private static boolean isLeap(int year){ if( year % 400 == 0 ) return true; if( year % 4 == 0 && year % 100 != 0 ) return true; return false; } public static void main(String[] args) { int year = 1901; int year_end = 2000; int find_day = 6; //Find Sunday (0 is Monday) int[] nonleap = {31,28,31,30,31,30,31,31,30,31,30,31}; int[] leap = {31,29,31,30,31,30,31,31,30,31,30,31}; int counter = 0; /*int day = 0; which is Jan 1 1900, Monday setup the date - (the day before "var year") */ int setup_year = 1900; int day = 0; while(setup_year < year){ int[] months = isLeap(year) ? leap : nonleap; for(int month : months){ day += month; } setup_year ++; } while(year <= year_end){ int[] months = isLeap(year) ? leap : nonleap; for(int month : months){ if((day+1)% 7 == find_day) counter ++;//Find first "day" of each month day += month; } year ++; } System.out.println(counter); } } ```