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Need some help!!

juan cuesta
Greenhorn

Joined: Oct 28, 2011
Posts: 3
HI people, Im student of sotware development, Im triying to solve this excersise and im stack , i hope someone can help me! thank you ;)


Algorithm 4.1. PrefixAverages1(X)
Input: X- a 1-D numerical array of size n
1) Let A = an empty 1-D numerical array of size n
2) For i = 0 to n-1
3) Let s = X[0]
4) For j = 1 to i
5) Let s = s + X[j]
6) End For
7) Let A[i] = s /(i+1)
8) End For
Output: An n-element array A of numbers such that A[i]
is the average of elements X[0],X[1], … ,X[i]

Algorithm 4.2. PrefixAverages2(X)
Input: X- a 1-D numerical array of size n
1) Let A = an empty 1-D numerical array of size n
2) Let s = 0
3) For i = 0 to n-1
4) Let s = s + X[i]
5) Let A[i] = s / (i+1)
6) End For
Output: An n-element array A of numbers such that A[i]
is the average of elements X[0],X[1], … ,X[i]

Exercise 1: Computational Complexity

1) What is the difference between the two algorithms? Read these two algorithms carefully. If necessary, it might be helpful to set up an array yourself and apply these two algorithms on it by running through them by hand for small size values of n.
2) Analyse both algorithms by counting primitive operations and derive T(n) for both algorithms. What is the time complexity (Big-Oh, O(n)) of each algorithm? Which one is the most efficient?

Exercise 2: Implementation

Implement the two algorithms in Java and perform a thorough experimental analysis of their running times. Plot their running times as a function of their input size as scatter plots. Choose representative values of the size n, and run at least 5 tests for each size value n in your tests.


Jesper de Jong
Java Cowboy
Saloon Keeper

Joined: Aug 16, 2005
Posts: 14269
    
  21

Hello Juan, and welcome to the Ranch!

Can you please explain how far you got with these exercises and where you got stuck? We're happy to help you here, but we're not going to do all of your homework for you. If you've started writing some code and it doesn't work like you expected, or you get an error, then please post your code and explain exactly what it does and how that differs from what you expected, or what the error exactly is.


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Campbell Ritchie
Sheriff

Joined: Oct 13, 2005
Posts: 39409
    
  28
By the way, which language is that? It looks rather like BASIC which I learnt 40 years ago.
Matthew Brown
Bartender

Joined: Apr 06, 2010
Posts: 4422
    
    8

I'd guess it's meant to be a pseudo-language - it's just to illustrate the algorithm, not to be actually runnable.

Have you gone through it by hand for some small numbers, as the question advises you to do? That would be the best starting point, to make sure you actually understand what it's doing.
 
Consider Paul's rocket mass heater.
 
subject: Need some help!!