Next Run Time of a Cron Job
Given a cron expression expr and a UTC timestamp afterIso (like 2024-03-08T09:00:00Z, possibly with non-zero seconds), return the first whole minute strictly after afterIso at which the job runs, formatted as YYYY-MM-DDTHH:MM:00Z.
The expression has five fields: minute (0-59), hour (0-23), day of month (1-31), month (1-12) and day of week (0-7, 0 and 7 are Sunday). Each field is a comma-separated list of *, n, a-b, or */a-b followed by /s. Minute, hour and month must match. For the day, if both day-of-month and day-of-week are restricted (anything other than exactly *), either one matching is enough; otherwise both must match.
Search at most 5 years (1830 days) ahead, starting from the day of afterIso. If no run is found, return null.
Example 1
Input: expr = "*/15 * * * *", afterIso = "2024-03-11T09:07:00Z" Output: "2024-03-11T09:15:00Z" Explanation: The next quarter hour.
Example 2
Input: expr = "0 9 * * 1-5", afterIso = "2024-03-08T09:00:00Z" Output: "2024-03-11T09:00:00Z" Explanation: Friday 09:00 itself is not strictly after, so the next weekday run is Monday.
Constraints
- expr is valid
- afterIso is between 1971 and 2094
Hint 1
Do not test every minute; skip whole days that do not match first.
Hint 2
Within a matching day, try the allowed hours and minutes in ascending order.
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Good practice for: Site Reliability Engineer, DevOps Engineer, Cloud Engineer, Backend Developer, Automation Test Engineer, Data Engineer
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