Python, Generating random string of brackets

Question

I am looking to generate random lengths and patterns of square brackets for example, [] ][ [] ][ [] [[ ]] []

I have so far managed to get my program to generate brackets randomly, but randomly in terms of how many times it generates them, so currently my program is giving me results such as,

[] [] [] [] [] []

[] [] []

[] [] [] [] []

So there is no randomness within the brackets, only randomness in the number of brackets displayed.

I want to know how I can make the order of the brackets random ASWELL as the amount of brackets on show.

Here is my code so far,

import random
import string

def randomGen(N):
    return random.randint(1,N)

char1 = '['
char2 = ']'
finalist = []
newList = []
newList2 = []

newValue = randomGen(99)

for i in range(newValue):
    newList = char1
    newList2 = char2
    finalist.append(newList + newList2)

for everChar in finalist:
    print everChar,

Thanks.

score 4 · Accepted Answer · answered Feb 25 '14 at 16:07

You could use random.sample to select the index for where to place, say, left brackets. Then place right-brackets everywhere else:

In [119]: import random

In [122]: N = 10

In [125]: idx = set(random.sample(range(N), N//2))

In [126]: idx
Out[126]: {0, 1, 4, 5, 7}

In [127]: ''.join(['[' if i in idx else ']' for i in range(N)])
Out[127]: '[[]][[][]]'

Given your examples, I assumed you want an equal number of left and right brackets. If not, use jonrsharpe's solution.

jonrsharpe · Answer 2 · 2014-02-25T16:12:44.713

4

You need to randomly choose from the two characters; you can do this all in one line:

 finallist = [random.choice('[]') for _ in range(random.randint(1, 99))]

You can also simplify the output:

print " ".join(finallist)

An example I just ran:

[ ] ] [ [ [ ] [ ] ] [

edited Feb 25 '14 at 16:12

answered Feb 25 '14 at 16:07

jonrsharpe

115,751
26
228
437

4

`random.choice('[]')` would do just fine, and seems more readable to me. – lanzz Feb 25 '14 at 16:10
I would have preferred `"".join(random.choice('[]') for _ in range(random.randint(1, 99)))` :) – thefourtheye Feb 25 '14 at 16:16
@thefourtheye for one line? because [`join()` works faster on list](http://stackoverflow.com/questions/9060653/list-comprehension-without-python/9061024#9061024) instead of genexps – Grijesh Chauhan Feb 25 '14 at 16:18
@GrijeshChauhan Oh yeah, I read that recently only. Thanks for reminding me :) – thefourtheye Feb 25 '14 at 16:19

score 4 · Answer 3 · answered Feb 25 '14 at 16:10

4

Well, if you just want to fix your code, you can simply do

finalist = list("".join(finalist))
random.shuffle(finalist)
for everChar in finalist:
    ...

If you want efficient and better ways, please have a look at the other answers.

answered Feb 25 '14 at 16:10

thefourtheye

233,700
52
457
497

score 1 · Answer 4 · answered Feb 25 '14 at 16:09

import random
import string

def randomGen(N):
    return random.randint(1,N)

length_to_generate = randomGen(99)
finalist = []
for i in range(length_to_generate):
    if random.randint(0, 1):
        finalist.append("[")
    else:
        finalist.append("]") 

for everChar in finalist:
    print everChar,

You can also generate a string rather than a list:

length_to_generate = randomGen(99)
finalist = ""
for i in range(length_to_generate):
    if random.randint(0, 1):
        finalist += "]"
    else:
        finalist += "["

print finalist

I have managed to get mine working using help from a friend, however I was also looking for my program to tell the user whether the results are balanced or unbalanced. By this I mean [ ] [ ] [ ] (Balanced) and [ ] [ [ [ ] [ ] (Unbalanced). Any idea how I would go about implementing this? — Baileyavfc, Feb 25 '14 at 16:32

Python, Generating random string of brackets

4 Answers4

Linked