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Professor F. Lake tells his class that it is asymptotically faster to square an -bit integer than to multiply two n-bit integers. Should they believe him?

Short Answer

Expert verified

No, the statement of Professor F. Lake is wrong.

Step by step solution

01

Introduction

Evaluate the following details:

• The algorithm's execution time is determined using asymptotic notations.

• According to the Professor, the n-bit integer algorithm squaring is faster than multiplying two n-bit integers.

• The algorithm's asymptotic value is determined by the number of items and actions in the algorithm.

02

Correct Fact

“No”, students should not believe the professor.

Description:

• When an n-bit integer is squared, numerous cross-terms become equal.

• As a result, there's no need to do it again.

• Take the 3-bit integer "1012" as an example.

• This number is written as a2, a1 , and a0 from left to right.

• If you square this number, you'll obtain 9 terms.

• In the matrix below, the terms are listed.

a2a2a2a1a2a0a1a2a1a1a1a0a0a2a0a1a0a0

• This is a symmetric matrix. Because the primary diagonal's components are all the same.

• In other words, certain elements do not require calculation.

• As a result, this approach for squaring n-bit values is not asymptotically superior.

• This algorithm will benefit from a steady pace.,

As a result, Professor is incorrect in his assertion that the fast-squaring method may be improved at a constant pace.

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Most popular questions from this chapter

In justifying our matrix multiplication algorithm (Section 2.5), we claimed the following block wise property: if X and Y are n×nn matrices, and

X=[ABCD],Y=[EFGH],

where A,B,C,D,E,F,G, and H are n/2×n/2 sub-matrices, then the product XY can be expressed in terms of these blocks:

XY=[ABCD][EFGH]=[AE+BGAF+BHCE+DGCF+DH]

Prove this property.

Question: On page 66 there is a high-level description of the quicksort algorithm.

(a) Write down the pseudocode for quicksort.

(b) Show that its worst - case running time on an array of size n is Θ(n)2.

(c) Show that its expected running time satisfies the recurrence relation.

T(n)O(n)+1ni=1n-1(Ti+Tn-i)

Then, show that the solution to this recurrence is O(nlogn).

In Section 2.1 we described an algorithm that multiplies two n-bit binary integers x and y in time na, where a=log23. Call this procedure fast multiply (x,y).

(a) We want to convert the decimal integer 10n(a 1 followed by n zeros) into binary. Here is the algorithm (assume n is a power of 2):

function pwr2bin(n)

if n = 1: return10102

else:

z= ???

return fastmultiply(z,z)

Fill in the missing details. Then give a recurrence relation for the running time of the algorithm, and solve the recurrence.

(b) Next, we want to convert any decimal integer x with n digits (where n is a power of 2) into binary. The algorithm is the following:

function dec2bin(x)

if n=1: return binary [ x ]

else:

split x into two decimal numbers xt,xRwith n/2 digits each

return ???

Here binary [.] is a vector that contains the binary representation of all one-digit integers. That is, binary role="math" localid="1659333641173" [0]=02, binary [1]=12, up to binary [9]=10012. Assume that a lookup in binary takes 0(1) time. Fill in the missing details. Once again, give a recurrence for the running time of the algorithm, and solve it.

In our median-finding algorithm (Section 2.4), a basic primitive is the split operation, which takes as input an array S and a value V and then divides S into three sets: the elements less than V , the elements equal to V , and the elements greater than V . Show how to implement this split operation in place, that is, without allocating new memory.

Given a sorted array of distinct integersA[1,...,n] , you want to find out whether there is an indexi for which A[i]=i. Give a divide-and-conquer algorithm that runs in time O(logn).

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