思路：算出2011年11月11日到1599年1月1日的天數，再算出要求的日期到1599年1月1日的天數，2個作差對7取余即可求出星期幾

AC代碼：

import java.util.Scanner;public class Main {		static int[] mon = {0,31,28,31,30,31,30,31,31,30,31,30,31};	public static void main(String[] args) {		Scanner in = new Scanner(System.in);		int year = in.nextInt();		int month = in.nextInt();		int day = in.nextInt();		int sum1 = cal(2011,11,11);		int sum2 = cal(year,month,day);		if(sum1 <= sum2) {			int sum = (sum2 - sum1 + 12) % 7;			if(sum == 0)				sum = 7;			System.out.PRintln(sum);		} else {			int sum = (sum1 - sum2) % 7;			if(sum == 0)				System.out.println(5);			else if(sum == 1)				System.out.println(4);			else if(sum == 2)				System.out.println(3);			else if(sum == 3)				System.out.println(2);			else if(sum == 4)				System.out.println(1);			else if(sum == 5)				System.out.println(7);			else if(sum == 6)				System.out.println(6);		}	}		public static int cal(int year,int month,int day) {		int sum = 0;		//注意這里是i<year		for(int i=1599; i<year; i++) {			if((i % 4 == 0 && i % 100 != 0) || (i % 400 == 0)) {				sum += 366;			} else {				sum += 365;			}		}		//注意這里是i<month		for(int i=1; i<month; i++) {			//是閏年的第二月，天數是29天			if(((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) && i == 2)				sum += mon[i] + 1;			else				sum += mon[i];		}		sum += day;		return sum;	}}