Minimum Amount of Time to Fill Cups
Necessary conditions are the minimum requirements that must be met for a certain result to be achievable. They establish the lower bound of the problem, or the minimum value the result can possibly be.
Here are the necessary conditions for this problem:
res >= max(A)
: This means that the minimum number of seconds to fill up all the cups (res
) should be greater or equal to the maximum number of cups of any type (max(A)
). This is because we can fill at most one cup of a particular type of water each second. Therefore, at the very least, it would take the same number of seconds as the highest amount of a single type of cup to fill up everything.res >= ceil(sum(A) / 2)
: This means that the minimum number of seconds to fill up all the cups (res
) should also be greater or equal to half the total number of cups, rounded up (ceil(sum(A) / 2)
). This is because we can fill up to two cups every second, one of each type. So, the quickest we could possibly fill up all cups is in half the total number of cups (rounded up), by filling two cups each second.
The sufficient condition refers to a strategy or condition that would be enough to achieve the desired result. In this case, one strategy is to always choose to fill up two cups of the types of water that we have the most cups left. This strategy will fill up all the cups in the fewest possible seconds.
The conclusion of this analysis is that the necessary conditions can be met, so they represent the minimum number of seconds needed to fill up all cups. The strategy of always filling two cups of the types of water that we have the most cups left achieves this minimum.

