Count how many times in D minutes a 12-hour clock shows a time whose digits form an arithmetic sequence, starting at 12:00 inclusive.
Medium4MathSimulationImplementationBrute forceNo attempts yetTime limit1sMemory limit512 MBWendy has an LED clock radio with a 12-hour display, showing times from 12:00 to 11:59. The hour carries no leading zero, but the minutes may carry one, as in 2:07 or 11:03.
When Wendy looks at the clock, she likes to spot times whose digits form an arithmetic sequence. Two of her favourite times are 12:34 and 2:46, because their digits form such a sequence.
A sequence of digits is an arithmetic sequence when every digit after the first equals the previous digit plus one fixed common difference. The sequence 1, 2, 3, 4 has common difference 1, and 2, 4, 6 has common difference 2.
Wendy starts watching at noon, the moment the clock reads 12:00, and watches it for D minutes. How many times during that period does the clock display a time whose digits form an arithmetic sequence?
The input contains one integer D, the number of minutes the clock is watched (0≤D≤109).
Print how many times a qualifying time is displayed, counting from 12:00 up to the moment D minutes later and including that final moment. Each displayed minute counts once, so a time that comes around again 12 hours later is counted again.
In the three hours after noon the qualifying times are 12:34 (common difference 1), 1:11 (common difference 0), 1:23 (common difference 1), 1:35 (common difference 2), 1:47 (common difference 3), 1:59 (common difference 4), 2:10 (common difference -1), 2:22 (common difference 0), 2:34 (common difference 1), 2:46 (common difference 2) and 2:58 (common difference 3), eleven in all.