CODEWITHSUNDEEP
python
Oliver
Oliver

Reputation: 323

How to reverse a stack without returning anything

a={}#dictionary
b=0
while(stack.is_empty()==False):
    b=b+1
    a={b:stack.pop()} 
else:
    for i in range(b, 0, -1):
       stack.push(a[i])

I think this should work but it doesn't, Key error and empty stack errors are raised

Upvotes: 0

Views: 70

Answers (3)

Za Noza
Za Noza

Reputation: 458

If I correctly understood, try

>>> {'b':[1, 2, 3, 4, 5][::-1]}
{'b': [5, 4, 3, 2, 1]} #list inside a dictionary are reversed

Upvotes: 0

SonicARG
SonicARG

Reputation: 517

For reversing a stack, you can consider the stack as a list and do:

stack.reverse()

instead of popping and pushing in a spare stack. From Python 2 documentation:

Reverse the elements of the list, in place

>>> a = [66.25, 333, 333, 1, 1234.5]
>>> a.reverse()
>>> a
[333, 1234.5, 1, 333, -1, 66.25]

EDIT: As rephrased by the questioner, if you want to reverse a stack into a new one, you can do:

def reverse_and_return(stack):
  newstack = []  # New list/stack
  for element in stack:
    newstack.insert(0, element)  # Push new element first
  return newstack

Upvotes: 1

John Kugelman
John Kugelman

Reputation: 362187

a={b:stack.pop()}

That will replace a with a new dictionary each iteration. To add keys to the existing dictionary, do

a[b] = stack.pop()

Upvotes: 0

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