c++ - On what days does the thirteenth occur? USACO -

is friday 13th unusual event?

that is, 13th of month land on friday less on other >day of week? answer question, write program compute frequency 13th of each month lands on sunday, monday, tuesday, >wednesday, thursday, friday, , saturday on given period of n years. >time period test january 1, 1900 december 31, 1900+n-1 >given number of years, n. n positive , not exceed 400.

here's have:

#include <iostream> #include <fstream> #include <string> #include <vector>  using namespace std; int main(){     ifstream fin("fridayin.txt");     ofstream fout("fridayout.txt");     int n;     fin >> n;     int current_year, end_year = 1900 + n - 1, current_day = 1; //set current_year, end_year, , current_day 1(monday)     int daycounter[7] = { 0 };  //this record how many times day occurs on 13th     int current_month = 1;     int day;     (current_month = 1; current_month <= 12; current_month++){         (current_year = 1900; current_year <= end_year; current_year++){    //jan 13=saturday             int yp = current_year - 1900;             if (current_year < 2000){   //2000 leap year                  day = (6 + yp + yp / 4 - yp / 100) % 7;                 daycounter[day]++;  //increment day counter             }             else if (current_year > 2000){  //check if it's after 2000, if add 1 6 0 (mod 7)                 day = (yp + yp / 4 - yp / 100) % 7;                 daycounter[day]++;  //increment day counter             }         }     }     int i;     (i = 0; < 7; i++){         fout << daycounter[i] << ' ';     }       return 0; } 

i'm computing january 13ths february 13ths,... december 13ths.

here's input:

20 

correct output:

36 33 34 33 35 35 34 

my output:

48 36 36 24 24 36 36  

i think know what's wrong, since january 13th, 1900 saturday made 6 mod 7 that's not true february 13th, 1900 , other months. i'd have change equations , create if statement that'd extremely long.

here's java implementation:

package time;  import java.text.dateformat; import java.text.parseexception; import java.text.simpledateformat; import java.util.calendar; import java.util.linkedhashmap; import java.util.map;  /**  * superstition calculates how 13th falls on each day of week  * @author michael  * @link https://stackoverflow.com/questions/31231343/on-what-days-does-the-thirteenth-occur-usaco  * @since 7/5/2015 10:31  */ public class superstition {      public static final dateformat default_format = new simpledateformat("yyyy-mmm-dd");     public static final int default_max_years = 400;     public static final string start_date = "1900-jan-13";     public static final int months_per_year = 12;       public static void main(string[] args) {         map<integer, integer> frequencies = new linkedhashmap<integer, integer>() {{             put(calendar.sunday, 0);             put(calendar.monday, 0);             put(calendar.tuesday, 0);             put(calendar.wednesday, 0);             put(calendar.thursday, 0);             put(calendar.friday, 0);             put(calendar.saturday, 0);         }};         try {             int maxyears = args.length > 0 ? integer.parseint(args[0]) : default_max_years;             calendar calendar = calendar.getinstance();             calendar.settime(default_format.parse(start_date));             (int = 0; < maxyears; ++i) {                 (int j = 0; j < months_per_year; ++j) {                     int dayofweek = calendar.get(calendar.day_of_week);                     frequencies.put(dayofweek, (frequencies.get(dayofweek) + 1));                     calendar.add(calendar.month, 1);                 }             }         } catch (parseexception e) {             e.printstacktrace();          } {             system.out.println(frequencies);         }     } } 

here's output years 1900 2300:

com.intellij.rt.execution.application.appmain time.superstition {1=687, 2=685, 3=685, 4=687, 5=684, 6=688, 7=684}  process finished exit code 0 

as expected, frequencies 13th falls on each day of week same. sum of values equals (# years)*(12 months per year), should be.