Distinct Subsequences
Count distinct subsequences of s that equal t Example: s = "rabbbit", t = "rabbit" => 3 (rabb)b(it), (ra)b(bbit), (rab)b(bit) Example: s = "babgbag", t = "bag" => 5
Distinct Subsequences is about turning repeated work into a reusable state instead of re-solving subproblems. It's a hard one for a reason: it stresses state-and-transition thinking when the rules pile up. Once you define the right state, the transitions usually write themselves.
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