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        riddles >> cs >> copy paste problem
        
(Message started by: alexeigor on Jan 20^th, 2011, 8:39am)

Title: copy paste problem
Post by alexeigor on Jan 20^th, 2011, 8:39am

Write a program to print the sequence of keystrokes such that it generates the maximum number of character 'A's. You are allowed to use only 4 keys: A, Ctrl+A, Ctrl+C and Ctrl+V. Only N keystrokes are allowed. All Ctrl+ characters are considered as one keystroke, so Ctrl+A is one keystroke.

For example, the sequence A, Ctrl+A, Ctrl+C, Ctrl+V generates two A's in 4 keystrokes.

* Ctrl+A is Select All
* Ctrl+C is Copy
* Ctrl+V is Paste

Title: Re: copy paste problem
Post by towr on Jan 20^th, 2011, 9:52am

[hide]function foo(n)
{
a = [0,1,2,3,4,5,6,9,12,16,20,27,36,48,64,81];
if ( n <= 15 )
return a[n];
else
n -= 11;
d = n % 5;
f = (n-d)/5;
return a[d+11] << (2*f);
}
[/hide]

Title: Re: copy paste problem
Post by birbal on Jan 25^th, 2011, 5:20am

on 01/20/11 at 09:52:27, towr wrote:

[hide]function foo(n)
{
a = [0,1,2,3,4,5,6,9,12,16,20,27,36,48,64,81];
if ( n <= 15 )
return a[n];
else
n -= 11;
d = n % 5;
f = (n-d)/5;
return a[d+11] << (2*f);
}
[/hide]

Nice solution :). Can you explain how did you reach at this solution ? ( As in by mere observation of the series or any mathematical way ? )

Title: Re: copy paste problem
Post by towr on Jan 25^th, 2011, 9:04am

By mere observation.
For good measure, it really ought to be proved correct. Maybe I'll get around to that eventually.

Title: Re: copy paste problem
Post by birbal on Jan 27^th, 2011, 4:28am

i think we can form a recurrence relation and solve it. Need to work out what exactly is to be done.

Title: Re: copy paste problem
Post by Grimbal on Jan 28^th, 2011, 8:40am

One thing still bothers me. As I know it,
- ctrl-C copies the selected text to the paste buffer without unselecting it
- ctrl-V replaces the selected text with the paste buffer
So, the sequence A, ctrl-A, ctrl-C leaves one A selected, and ctrl-V replaces it with the A from the paste buffer. It doesn't result in 2 A's.

I daily duplicate lines of text by selecting the lines and pressing ctrl-C, ctrl-V, ctrl-V. The first ctrl-V having the effect of unselecting the selection.

Title: Re: copy paste problem
Post by towr on Jan 28^th, 2011, 11:48am

It would depend on the editor.
In any case, you can consider that you are given 4 operations to work with, and "replace" is not among them (nor implied by their description).