# Loops

Chris Pocock

Greenhorn

Posts: 13

posted 14 years ago

I was just wondering, how would you write a for loop to decode a String by trying every possible combination of numbers/letters?

eg.

Something like that I guess. I'm still trying to figure out this problem. Can anybody help me or give me any hints? Am I doing this totally wrong?

Thanks

-Chris

[ April 03, 2002: Message edited by: Chris Pocock ]

eg.

Something like that I guess. I'm still trying to figure out this problem. Can anybody help me or give me any hints? Am I doing this totally wrong?

Thanks

-Chris

[ April 03, 2002: Message edited by: Chris Pocock ]

<i>I'm currently reading 'How to program Java' by Deitel</i><br /><b>I am still learning, so be kind. I also know C++, by the way</b>

James Swan

Ranch Hand

Posts: 403

posted 14 years ago

There were a couple of cool algorithms posted yesterday by Brent Worden for performing combinations and permutations (implemented in C++ too).

They could be well worth a look.

http://www.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=33&t=005058

James.

They could be well worth a look.

http://www.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=33&t=005058

James.

Chris Pocock

Greenhorn

Posts: 13

posted 14 years ago
<i>I'm currently reading 'How to program Java' by Deitel</i><br /><b>I am still learning, so be kind. I also know C++, by the way</b>

The algorithm from that link that was in that guys post didn't look like it would help me out... I edited my original post to make the code better (I was in a rush before).

I'm still (very) open to

Thanks heaps

-Chris

I'm still (very) open to

**any**help .Thanks heaps

-Chris

James Swan

Ranch Hand

Posts: 403

posted 14 years ago

I thought those algorithms were almost spot on for what you're trying to do (brute force approach).

If you look at a definition of what a permutation is (it's been 10 or so years so I did Mathematics so I had to look it up):

http://mathforum.org/dr.math/faq/faq.comb.perm.html

Those algorithm's will return you the possible values in a permutation (given the right input).

Ok, as I said my math is a little out but Ill give it a shot anyway.

Lets say you have a "password" of length 5, that can be any combination of "lowercase letters" and numbers (ie. a..z 0..9)

So the number of possible permutations of that password is:

36_P_5 = 36! / (36 - 5)! = 45,239,040

My understanding that those algorithms posted would actually return in each iteration a particular set of values.

In the above case there would be ~45 Million iterations.

Please feel free to flame if my Math is incorrect.

If you look at a definition of what a permutation is (it's been 10 or so years so I did Mathematics so I had to look it up):

http://mathforum.org/dr.math/faq/faq.comb.perm.html

Those algorithm's will return you the possible values in a permutation (given the right input).

Ok, as I said my math is a little out but Ill give it a shot anyway.

Lets say you have a "password" of length 5, that can be any combination of "lowercase letters" and numbers (ie. a..z 0..9)

So the number of possible permutations of that password is:

36_P_5 = 36! / (36 - 5)! = 45,239,040

My understanding that those algorithms posted would actually return in each iteration a particular set of values.

In the above case there would be ~45 Million iterations.

Please feel free to flame if my Math is incorrect.

James Swan

Ranch Hand

Posts: 403

posted 14 years ago

Ok I had to try it for myself:

You should get output:

[ April 04, 2002: Message edited by: james swan ]

You should get output:

**Your password was js1, guessed after 11314 tries**[ April 04, 2002: Message edited by: james swan ]