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I have an unknown string S of length n. I have to given small string A1 and A2. Supposed that I know the probability of S.contains(A1) = true (which mean A1 appears in S at least once) and S.contains (A2) = true.

How do we compute the probability of S.contains(A1) && S.contains(A2)?

The general problem: Compute the probability P[S.contains(A1) && S.contains(A2) && ... && S.contains(An)] when we know P[S.contains(A1)], P[S.contains(A2)], ..., P[S.contains(An)]

Thank you

Update: We can compute P[S.contains(x) == true] in which x is an arbitrary string.

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1 Answer 1

I guess if intersection of A1 and A2 is 0, then you should simply multiply the Pr(A1) and Pr(A2). or if you know probability of S.contains(A1) or S.contains(A2) you can simply subtract it from P(S.contains(A1) + p(S.contains(A2))

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What do you mean by intersection of A1 and A2? For example, if A1 = '101' && A2 = '000', then if you mean the intersection is the part X that either is prefix of A1 and postfix of A2 or prefix of A2 and postfix of A1, then this case the intersection is blank. Then in case n = 5, we have P(S.contains(A1)) > 0, P(S.contains(A2) > 0 but P(S.contains(A1) && S.contains(A2)) = 0 –  Loi.Luu Sep 6 '13 at 8:37
    
I know nothing more than the given assumption :) –  Loi.Luu Sep 6 '13 at 8:40
    
So what if we have A and B do not intersect? –  Loi.Luu Sep 9 '13 at 2:27

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