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Arrays: Left Rotation

  • asfaltboy + 2 comments

    True. However, it becomes an elegant solution if we use collections.dequeue instead of list. Double ended queues have a popleft method, which is an O(1) operation:

    def array_left_rotation(a, n, k):
    for _ in range(k):
        a.append(a.popleft())
    return a

    More info: https://wiki.python.org/moin/TimeComplexity#collections.deque https://docs.python.org/3/library/collections.html#collections.deque

    • AffineStructure + 1 comment

      They have rotate built into the deque

      def array_left_rotation(a, n, k):
    a = deque(a)
    for i in range(k):
        a.rotate(-1)
    return a
      • josegabriel_st + 0 comments

        You have O(n) in:

        a = deque(a)

        In order to avoid this, you should use a deque from the beginning like:

        from collections import deque

def array_left_rotation(a, n, k):
    a.rotate(-k)

n, k = map(int, input().strip().split(' '))
a = deque(map(int, input().strip().split(' ')))
array_left_rotation(a, n, k);
print(*a, sep=' ')

        And array_left_rotation only takes O(k) instead of O(n).

        Note that a is pased by reference, so there is no need to return anything, but this could be an issue for some user cases, for this particular problem, it works.

    • julianesteban2p1 + 0 comments

      i'd change '''for _ in range(k%len(a)) ''' to be more eficent