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| function monthDays(year){ | |
| const m = (new Array(12)).fill(1).map((_,x)=>x%2?30:31); | |
| if (year % 4) m[1] = 28; | |
| else if (year % 100) m[1] = 29; | |
| else if (year % 400) m[1] = 28 | |
| else m[1] = 28; | |
| return m; | |
| } | |
| function firstSundays(start, end){ | |
| let r = 0; | |
| let sundays = 0; | |
| for (let y = 1900; y < end; y++){ | |
| for (let days of monthDays(y)){ | |
| r = (days + r) % 7; | |
| if (r === 0 && y >= start) sundays++ | |
| } | |
| } | |
| return sundays; | |
| } |
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