Left Rotation on an Array

Question

I have a question where I need to rotate an array left k times.

i.e. if k = 2, [1, 2, 3, 4, 5] . -> [3, 4, 5, 1, 2]

So, my code is:

def array_left_rotation(a, n, k):
    for i in range(n):
        t = a[i]
        a[i] = a[(i+n-1+k)%n]
        a[(i+n-1+k)%n] = t

    return a

where n = length of the array.

I think the problem is a mapping problem, a[0] -> a[n-1] if k = 1.

What is wrong with my solution?

Answer 1

Another way to do this with the help of indexing is shown below..

def rotate(l, n):
    return l[n:] + l[:n]

print(rotate([1, 2, 3, 4, 5], 2))

#output : [3, 4, 5, 1, 2]

This will only return the original list if n is outside the range [-len(l), len(l)]. To make it work for all values of n, use:

def rotate(l, n):
  return l[-n % len(l):] + l[:-n % len(l)]

Answer 2

def leftRotation(a, d, n):
    i=0
    while i < n:
        print (a[(i+d)%n], end = ' ')
        i+=1
    return i

if __name__ == '__main__':
    a =[1, 2, 3, 4, 5, 6, 7]
    d = 4
    n = 7 or len(a)
    leftRotation(a, d, n)

This is how I solved my hackerrank left rotation challenge