# friday

【题目描述】

Friday the Thirteenth
Is Friday the 13th really an unusual event? That is, does the 13th of the month land on a Friday less often than on any other day of the week? To answer this question, write a program that will compute the frequency(频率) that the 13th of each month lands on Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday over a given period of N years. The time period to test will be from January 1, 1900 to December 31, 1900+N-1 for a given number of years, N. N is positive(积极的) and will not exceed(超过) 400. Note that the start year is NINETEEN HUNDRED, not 1990. There are few facts you need to know before you can solve this problem: January 1, 1900 was on a Monday. Thirty days has September, April, June, and November, all the rest have 31 except for February which has 28 except in leap(飞跃) years when it has 29. Every year evenly divisible(可分的) by 4 is a leap year (1992 = 4*498 so 1992 will be a leap year, but the year 1990 is not a leap year) The rule above does not hold for century years. Century years divisible by 400 are leap years, all other are not. Thus, the century years 1700, 1800, 1900 and 2100 are not leap years, but 2000 is a leap year. Do not use any built-in(嵌入的) date functions in your computer language. Don't just precompute the answers, either, please. 【我的思路】 1.第 N 个月的 13 号的星期数取决于上个月的天数和上个月 13 号的星期数。 2.要考虑到 1 月和 2 月的特殊情况。1 月没前驱，所以定义 0~11 月的天数，2 月有闰月，所 以要判定年份。 3.确定星期数的时候一定要取 mod。 4.还有，超坑爹的是它的题目要求的输出是从星期六到星期五，而我一开始就默认为从星期 一开始输出，结果找了好久…… 【code】 //2.3 Friday const day:array[0..11] of integer=(31,31,28,31,30,31,30,31,31,30,31,30); var n,i,j,s,last,today:integer; a:array[1..7] of integer; begin readln(n); fillchar(a,sizeof(a),0); s:=1899; last:=3; for i:=1 to n do begin inc(s); for j:=1 to 12 do

begin today:=(last+day[j-1] mod 7+6) mod 7+1; if ((s mod 4=0) and (s mod 100<>0) or (s mod 100=0) and (s mod 400=0)) and (j=3) then today:=(today+7) mod 7+1; inc(a[today]); last:=today; end; end; for i:=6 to 7 do write(a[i],' '); for i:=1 to 4 do write(a[i],' '); write(a[5]); End. Executing... Test 1: TEST OK [0.003 secs, 276 KB] Test 2: TEST OK [0.003 secs, 276 KB] Test 3: TEST OK [0.000 secs, 276 KB] Test 4: TEST OK [0.000 secs, 276 KB] Test 5: TEST OK [0.003 secs, 276 KB] Test 6: TEST OK [0.003 secs, 276 KB] Test 7: TEST OK [0.000 secs, 276 KB] Test 8: TEST OK [0.000 secs, 276 KB] All tests OK.

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