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Pierre's microwave has keys to input reheating time, with possible positive times described by the set K. For instance, we could have
K=\{1,10,60\}.
Pierre is wondering what the minimum number of keys to press to input the time t. Each key can be pressed multiple times.
For example, the minimum number of keys to press for a time t=25 is
7: pressing
10 twice and pressing
1 five times.
In order to solve this problem, we decompose the problem into subproblems defined as
minPresses[t]= {the minimum number of key presses required to input a time t using keys from
K}.
Give a recurrence relation for minPresses by giving all cases in the expression
minPresses[t] = \begin{cases} \text{first case}\\ \dots\\ \text{last case}, \end{cases}
(Recall that a recurrence relation needs at least one base case and one general case.)