CODEWITHSUNDEEP
pythonlistreverse
user3285099
user3285099

Reputation: 527

Is reversing part of python list in place

Does reversing part of the array in the following manner create a copy of array from i to j?

a[i:j] = a[i:j][::-1] # is this in place? Does this operation require O(j-i) space

Does following code not take any extra space?

a[i:j] = reversed(a[i,j])

So is there any other way to reverse part of list with O(1) space apart from following code?

for k in range(i, i + (j-i + 1)//2):
  arr[k], arr[j-k] = arr[j-k], arr[k]

Upvotes: 1

Views: 241

Answers (1)

chepner
chepner

Reputation: 530930

Kind of. a is modified in place, but a[i:j] creates a new list object, as does applying [::-1] to a[i:j].

b = a[i:j]  # new list object
b = b[::-1] # another new list object
a[i:j] = b  # modifies a in place

Upvotes: 3

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