Which of the following is the solution of the following recurrence relation T(n) = T(2n/3) + 1?

  1. θ(n2)
  2. θ(log n)
  3. θ(n log n)
  4. θ(n3/2)

Answer (Detailed Solution Below)

Option 2 : θ(log n)

Detailed Solution

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The correct answer is : option 2.

Key Points

Explanation of the Recurrence Relation Solution

Given the recurrence relation: T(n) = T(2n/3) + 1

To solve this, we will use the Master Theorem for divide-and-conquer recurrences of the form:

T(n) = aT(n/b) + f(n)

In our case, a = 1, b = 3/2, and f(n) = 1.

Using the Master Theorem, we compare f(n) with n^log_b(a):

  • a = 1
  • b = 3/2
  • log_b(a) = log(1) / log(3/2) = 0
  • f(n) = 1

Since f(n) = 1 is Θ(1), it matches the case where f(n) = Θ(n^c) with c = 0. This corresponds to case 2 of the Master Theorem, where f(n) is polynomially smaller than n^log_b(a).

Therefore, the solution to the recurrence is:

T(n) = Θ(log n)

Thus, the correct answer is option 2.

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