hw1-solns - Illinois Institute of Technology Department of...

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Illinois Institute of Technology Department of Computer Science Solutions to Homework Assignment 1 CS 430 Introduction to Algorithms Spring Semester, 2009 1. Problem 2.3-3 on page 36 Solution: The base case is when n = 2, and we have n lg n = 2lg2 = 2 · 1 = 2. For the inductive step, our inductive hypothesis is that T ( n /2) = ( n /2)lg( n /2). Then T ( n ) = 2 T ( n /2) + n = 2( n /2)lg( n /2) + n = n (lg n - 1) + n = nlgn - n + n = n lg n , which completes the inductive proof for exact powers of 2. 2. Problem 2.3-4 on page 37 Solution: Since it take Θ( n ) time in the worst case to insert A[ n ] into the sorted array A[1. . n -1], we get the recurrence T ( n ) = ½ Θ(1) if n = 1 T ( n - 1) + Θ( n ) if n > 1 The solution to this recurrence is T ( n ) = Θ( n 2 ) 3. Problem 2-3(a) on page 39 Solution: cost times 1 y 0 c 1 1 2 i n c 2 1 3 while i 0 c 3 n +1 4 do y a i + x · y c 4 n +1 5 i i - 1 c 5 n +1 The running time of the algorithm is the sum of running times for each statement executed:
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hw1-solns - Illinois Institute of Technology Department of...

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