Count distinct subsequence

#1

is this problem can be solved using top down dp…?

#2

Hi @nikhilmeena,
yes it can be solved using top down dp also.
u can use the following approach.
DP[i] = DP[i-1]*2 - DP[Immediate previous occurence of character S[i-1]], if S[i-1] has occurred before.
Try to think of how dis comes and try taking some examples.
if u feel like u r facing some problem, feel free to post ur doubt here.
If u want, i can provide d code for d problem as well.
But first try to think about the above relation.
Hope dis will help.

#3

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