歐拉計劃19--Counting Sundays

結果：171

#include<iostream>
using namespace std;

int main()
{
	int a[13]= {0,31,28,31,30,31,30,31,31,30,31,30,31};
	int day=1,ans =0;
	for(int i=1900;i<=2000;i++){
	    if((i%4==0&&i%100!=0)||(i%400==0)){
			a[2] = 29;
		}else{
			a[2]=28;
		}
		for(int j=1;j<=12;j++){
			day+=a[j];
			if(day%7==0&&i>1900){
				ans++;
			}
		}
	}
	cout<<ans<<endl;
	return 0;
}