Ace Test Series: Algorithms - Searching

Question

Comments

yes, it should be T(n) = T(2n/3) + 1

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1. i think T(n)=T(2n/3)+1

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in quick sort if you take 9-to-1 split then

T(n)=T(9n/10)+T(n/10)+cn

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I think its recurrence relation should be T(n) = T(2n/3) + T(n/3) + c.

So every time it gets splits into two-thirds and one-third.

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@Shubhanshu

in binary search, at every iteration we will throw away half array depending on(key<=A[mid] or key>A[mid]),

so the worst case recurrence relation will be T(n) = T(2n/3) + 1

you are taking T(n) = T(2n/3) + T(n/3) + c., which is not correct because if we choose to take T(2n/3), then we will throw away T(n/3), similiarly if we choose to take T(n/3), we will throw away T(2n/3)..

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Same question here: https://classes.soe.ucsc.edu/cmps102/Fall01/solutions4.pdf

Answer 1

Answer of this question should be

T(n) = T(2*n/3) + 1

because after split there are two possibilities

either T(n) = T(2*n/3) + 1 or T(n) = T(n/3) + 1,

because that element is either present in left side or in right side, not on both sides.

As we need to find the worst case so number of comparison holds this relation 2*n/3  > n/ 3 ,

so we take this case T(n) = T(2*n/3) + 1.