Suppose I have One set of numbers i.e
{1, 6, 3, 5, 7, 9}
I want to Generate Random number from this set of number only i.e. a Generated number should be random and should be from these number({1, 6, 3, 5, 7, 9}) only.
standard C/C++ function will also do...
arc4random%(set count) = a random index.
What they are telling you is this. Generate a random number from 0-5. Then use that as an index into the array. Eg if the random # is 2, look at element #2 (the third one since you start at 0) of your list of numbers, which is 3. If the random # is 5, you get 9.
MSalters' comment shows you how to do it in a single expression.
Related
Background
Hi, I'm trying to solve a programming problem and I'm stuck on the following problem:
Assume you have multiple lists of numbers. All are sorted in decreasing order.
You now have to take exactly one number from each list to make the biggest possible sum.
So far so easy, to solve this you could just take the first number of each list and you're done.
But now, I need the second-largest sum while still using exactly one number from each list.
To achieve this, I would take the first element in each list but for the list which has the least difference between the first and second number the second number will be used.
This is still pretty doable.
The Problem
But I need an Iterator over every possible sum using exactly one number of each list sorted in decreasing order.
For performance reasons, it isn't possible to just compute every sum and then sort it. The algorithm must already provide the sums in decreasing order. If there are multiple combinations for a sum then the sum must be returned multiple times.
Additional Requirements
The Iterator should be lazy (only calculate the next sum when required).
The Lists are already lazy, which means you should require as few values as possible to calculate the fitting sum.
Example
For the Lists:
List 1: [5, 2, 1]
List 2: [10, 2]
List 3: [6, 1]
The Iterator then should return:
[5, 10, 6] = 21
[2, 10, 6] = 18
[1, 10, 6] = 17
[5, 10, 1] = 16
[5, 2, 6] = 13
[2, 10, 1] = 13
[1, 10, 1] = 12
[2, 2, 6] = 10
[1, 2, 6] = 9
[5, 2, 1] = 8
[2, 2, 1] = 5
[1, 2, 1] = 4
Comment
I don't need code as an answer to my question (you're still welcome to provide it if it helps to explain). What I'm looking for are ideas to solve this, or solutions that I can implement myself.
Thanks in advance!
First of all, Thanks to wlui155 for the help.
For Anyone interested, I coded a BFS algorithm that acts as follows:
Definitions:
Entry: Struct containing indices of used numbers and sum
BSet: Ordered set which can only contain unique Entries
Algorithm:
Pop Entry with biggest sum from BSet
Create a clone for each list
Advance in each clone a different index by one
Put new entries in BSet
Print current Entry
Goto 1.
Now you only have to ensure that no entry appears again after you've popped it. This can be ensured with a separate set containing all combinations for the current sum. Once the current sum gets smaller this set can be cleared.
If you have ideas to improve this, you're welcome to tell me.
I need to make a list of numbers. These numbers represent binary masks. The first 100 or so masks are all included in this range. In the next group of masks only certain masks are included. I need a list similar to the following.
[1,2,3,5,6,7,8,9,10,30,34,48,53,62]
Can I do something like [range(1,10),30,34,48,53,62]
or do I need to create my list using range(1,10) and then append the next list to it?
Thanks
Python 3 actually allow you to build a list literal prepending an * to any iterable objects - which are in turn expanded in place:
>>> [1,2, *range(10), *range(2)]
[1, 2, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1]
If you need this n older Pythons, or if you'd prefer to keep readability for people not too proeficient in Python who might have to walk through your code, an option is just to concatenate your different list fragments using the + operator:
a = list(range(1,10)) + [ 30,34,48,53,62]
Looks like I had to use the list(range(1,10)+[47,34,57]
solution
I am dealing with somewhat of a mystery and hoped for some clarity. I wrote a script for finding dice roll combinations adding to 24 that looks like the following:
start=[3,3,3,3,3,3,3,3]
outcomes=set(tuple(start)) #Use a set to ensure uniqueness
index_list=np.random.randint(0,8,1000)
#This little snippet adds one and subtracts one randomly, keeping total at 24
for i in xrange(0,500):
upper=index_list[i]
downer=index_list[i+20]
if start[upper]!=6 and start[downer]!=1:
start[upper]=start[upper]+1
start[downer]=start[downer]-1
outcomes.add(tuple(start))
print outcomes
What I am running into, is that When I look at outcomes, there is a single 3 of type 'int' in there.
set([(4, 4, 4, 3, 2, 2, 2, 3), 3, (2, 5, 4, 3, 1, 4, 2, 3), (4, 4, 4, 2, 3, 1, 3, 3),(4, 2, 5, 2, 3, 4, 1, 3)])
While I could certainly remove it, I am just curious how it is getting in there to begin with? My initial guess was the index list might be producing an index outside of [0-7], but it is not. I've looked for a similar question other places, but have yet to find a similar issue. Thanks!
set expects an iterable. You're passing a tuple which is an iterable.
set iterates through it, leaving just 1 value: 3 (because your tuple only contains the same 3 value).
You have to put your element in a list or tuple so it is seen as a single element (exactly the same problem when you pass a string and it is unexpectedly iterated upon)
The rest of your code is OK and has nothing to do with the problem.
Do this instead:
outcomes=set([tuple(start),])
now set iterates through a list of 1 tuple, effectively creating tuple elements.
You could do that also, maybe simpler:
outcomes=set()
outcomes.add(tuple(start))
there's no ambiguity since you're adding 1 element. It's not iterated through.
Hi so I am trying to write a function hack() that takes no arguments and returns an iterator over all possible passwords.
Basically, I have to user an iterator to brute force a password. All I know from the question is that:
The password consists of three segments.
The first segment of the password is a concatenation of two words in the following list of words: ["hello", "BEGONE", "dog", "MrCool"]
The middle segment is "Donkey20"
And the last segment consists of two digits that together (i.e. 1 and 7 = 17), are no larger than 38. (And at least 0)
My method of thinking is this:
Find all the possible combinations of POSSIBLE_WORDS by using permutations(). (Find all segment 1 possibilities)
For each combination in the new list, add "Donkey20" to the end. (For example: helloBEGONEDonkey20)
Find all possible combinations between the elements in THAT list and POSSIBLE_NUMBERS.
Create an iterator that iterates over all these possible passwords, and return it
My current code only is able to do step 2, but instead of Donkey20 being at the end of each combination it's at the start. (e.g. Donkey20helloBEGONE instead of helloBEGONEDonkey20)
POSSIBLE_WORDS = ["hello", "BEGONE", "dog", "MrCool"]
MIDDLE = "Donkey20"
possible_numbers1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
possible_numbers2 = [16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28]
possible_numbers3 = [29, 30, 31, 32, 33, 34, 35, 36, 37, 38]
POSSIBLE_NUMBERS = possible_numbers1 + possible_numbers2 + possible_numbers3
from itertools import permutations, combinations
def hack():
first_words = [''.join(word) for word in permutations(POSSIBLE_WORDS, 2)]
first_words.append(MIDDLE)
first_half = [''.join(word) for word in permutations(first_words, 2)]
Any way to fix this issue? How do I finish the remainder of the steps? Is there a different approach I could use to code this program?
Any help would be very much appreciated!
First of all, there is no reason to build up POSSIBLE_NUMBERS like that. Just use range(39) or list(range(39)) instead.
Your intention in
first_words.append(MIDDLE)
was almost certainly not to tack the single word "Donkey20" onto the end of the list of all possible first parts but was instead to tack it onto the end of each first word. I think that your intention in that part of the code can be better expressed by getting rid of that line as well as the following line and just use the single line
first_half = [word + MIDDLE for word in first_words]
When you are putting together the final possible passwords, you are going to need to turn the numbers into strings. Doubtless you already know about str() but that function has the drawback that str(1) is '1' whereas you probably want '01'. In this context, you might want to use format() since format(1,'02') returns '01'.
This should be enough of a hint to get you going. Since this seems to be homework I don't want to say any more.
I want to multiply every item in a list. But this example just returns every item:
list = 1..10
println list.each{it*2}
Use collect().
i.e.
list = 1..10
println list.collect{it*2}
Gives
[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
Only the syntax of Groovy is pegged to be standardized, not the default methods, so different implementations of Groovy have different names for the specific method to use.
In Codehaus Groovy (v 2.1.9 at groovy.codehaus.org) use collect...
list = 1..10
println list.collect{it*2}
In Real Groovy (v 0.10.0 at realgroovy.codeplex.com) use the more standardly named map...
test{
is [1,2,3,].map{it*7} == [7,14,21]
}
I'm not sure how GrooScript (at www.grooscript.org) does it.