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);
        }
}