Practice - Maximum Points

Here's a practice problem: you have $n$ cards with values $v_1, v_2, \ldots, v_n$. You can take cards, but if you take card $i$, all cards with values $v_i - 1$ and $v_i + 1$ are destroyed. get the highest total points.

This is Boredom in disguise. Count the frequency of each value. The total points from taking all cards of value $x$ is $count[x] \times x$.

Now it's House Robber on the value array. Try coding it yourself. The key steps: count frequencies, find max value, run House Robber DP on the frequency array. Time: $O(n + M)$ where $M$ is the maximum card value. Space: $O(M)$ for the frequency array, or $O(1)$ with state compression.