I met this problem in codewars and I do not understand the solution from other users.
This is the question
Write a function which makes a list of strings representing all of the ways you can balance n pairs of parentheses
Examples
balanced_parens(0) => [""]
balanced_parens(1) => ["()"]
balanced_parens(2) => ["()()","(())"]
balanced_parens(3) => ["()()()","(())()","()(())","(()())","((()))"]
My solution involves using itertools permutations to get all permutations from input and adding them to a list. However, this will use up too much memory once n gets to 10.
this is the solution from another user.
def balanced_parens(n):
'''
To construct all the possible strings with n pairs of balanced parentheses
this function makes use of a stack of items with the following structure:
(current, left, right)
Where:
current is the string being constructed
left is the count of '(' remaining
right is the count of ')' remaining
'''
stack = [('', n, 0)]
result = []
# Loop until we run out of items in the stack
while stack:
current, left, right = stack.pop()
# if no '(' or ')' left to add, add current to the result
if left == 0 and right == 0:
result.append(current)
# if we can, add a '(' and return to the stack
if left > 0:
stack.append((current + '(', left - 1, right + 1))
# if we can, add a ')' and return to the stack
if right > 0:
stack.append((current + ')', left, right - 1))
return result
I do not understand how this code will cycle through all permutations.
From my understanding, I know that this code will add a ‘(‘ while in the loop, and a ‘)’ when there is an open ‘(‘. So n=3 will return ‘()()()’
But how does it cycle through the rest, eg ‘((()))’?
i tried looking through the comments for this answer. Other than saying that this is a very elegant solution, not much else was said. I was not able to understand much from chatgpt either.