When to Use Bitmask DP

Use bitmask DP when you see these signals:

$1.$ Small set size. $n \le 20$ is typical, since $2^{20} \approx 10^6$.

$2.$ Subset tracking. You need to know which items have been used.

$3.$ Order or assignment matters. TSP needs to track visited cities; assignment needs to track assigned tasks.

The state is $dp[mask]$ or $dp[mask][i]$ where $mask$ represents the subset and $i$ might be the last element.