private int minInSet(final TreeSet<Integer> set) {
		int previous = 0;
		int min = Integer.MAX_VALUE;
		boolean first = true;
		for (final int value : set) {
			if (first) {
				previous = value;
				first = false;
				continue;
			}
			else {
				final int diff = value - previous;
				if (diff < min) {
					min = diff;
				}
			}
		}
		return min;
	}
Advance the calendar to the particular hour paying particular attention
to daylight saving problems.

@param cal  the calendar to operate on
@param hour the hour to set
spring-cloud-alibaba-starters/spring-cloud-starter-alibaba-schedulerx/src/main/java/com/alibaba/cloud/scheduling/schedulerx/util/CronExpression.java