CS 61B Lecture 5: Iteration and Arrays I

[TheAhmedMAhmed]

Thank you Gentlemen;

{I will now go to have a wonder cup of English tea[]}

[eem553]

Arrays in java are objects...i agree of that... but where did they fit in the class hierarchy. any answer please..

[xwowsersx]

Wrote out the Sieve of Eratosthenes by hand to work through the algorithm. I used a boolean array of size 11 and ran through it by hand. Can't seem to see where the loop sets 9 to be false. I was left with 4, 6, 8, 10 set to false, and 2, 3, 5, 7, and 9 set to TRUE. But 9 is prime, so what am I missing here?

[spartanfry]

@xwowsersx 9 isn't prime...

[xwowsersx]

@spartanfry yea, i meant "but 9 ISN'T prime." Doesn't matter anyways...figured it long ago.

[spartanfry]

@xwowsersx Sorry about that, I did not notice this was posted a month ago until after I posted the comment.

[xwowsersx]

@spartanfry no worries. just cuz it was a month ago, doesnt mean i wasnt still struggling. thanks!

[Bharatwaj89]

good man with great knowledge......

[programmer1905]

8:34 his voice cracks =), what a great teacher this man is.

[wrdeboise]

I performed the sieve prime example and set 'n' to ten and it printed out all primes up to ten. Is that the correct result? I'm a Flash programmer so I simply changed the syntax for AS3.0 and wrote a class. Unfortunately, I don't think you can actually create a Boolean array in AS (possibly as a 'rest array' as a function argument and set the return value as Boolean(?)), so I simply created an array and set it to true in the 'for' loop.

[wrdeboise]

I think what looks like a field, in many cases, is actually a call to a getter method. Otherwise, how else would it be able to perform any useful function (?) If my logic is flawed, I'd like to be corrected.

[ngarcia65]

at around minute 2, it does not need to check all the numbers up until n, since the biggest divisor is always n/2, and this saves half the iterations on the while loop.

Its really not a very good example to a while loop, since it could be done simply by a for cycle. While loops are usually applied when you don't really know how many iterations you will have.

[DrGenius73]

Later in lecture he uses the sieve of Eratosthenes to implement a much faster way of finding a range of primes.

[amightyo]

ROck on!!!!

[cristianigianni]

extremely clear! Very interesting for students of Informatics.

[elcapino85]

He Made an error in 10:23 where he changes the IsPrime Method to use for Loop he forgot to Erase at the end the divisor++; because he has it in the for loop so it does not make sence to have divisor++; in the end of the program will not work like it suppose to!!

[skyflashings]

i saw that too, but the board was covering that extra divisor++ statement when he was writing the for loop...honestly, i don't know why he uses a chalkboard to write out all of his code anyway...

[0121ryanh117]

@skyflashings It makes a change to see someone that is prepared to spend their time writing it out by hand. If I did that, I would be non sensical becuase my writing is ass.

[jimed]

it looks like he left it in from when he did the while loop, you would need it there.

[availableaccount]

Doesn't the loop in the Pascal triangle method needs variables I and J for looping sake ?