CODEWITHSUNDEEP
pythonloopsif-statement
jmamath
jmamath

Reputation: 300

Python stop increment a list in certain condition

I am trying to implement a simple left rotation in a list. Please review the following code:`

def left_rotation(n,d,arr):
    temp = arr
    for i in range(n):
        print(temp[i])  # here is the problem
        if (i-d < 0):
            arr[i+n-d] = temp[i]
        else:
            arr[i-d] = temp[i]
    return arr
print(left_rotation(5, 4,[1,2,3,4,5]))

When I put the if-else structure it fails to access the variable temp but when I remove the if-else, it works. How do you explain that ?

Upvotes: 1

Views: 702

Answers (1)

Anurag A S
Anurag A S

Reputation: 731

temp = arr does not copy the list. It only creates a new reference which points to the same list. To copy you can use temp = arr[:]

def left_rotation(n,d,arr):
        temp = arr[:]
        for i in range(n):
            print(temp[i])  # here is the problem
            if (i-d < 0):
                arr[i+n-d] = temp[i]
            else:
                arr[i-d] = temp[i]
        return arr
    print(left_rotation(5, 4,[1,2,3,4,5]))

This should work. Sample Output1:

>>> print(left_rotation(5,2,[1,2,3,4,5]))
1
2
3
4
5
[3, 4, 5, 1, 2]

Sample Output2:

>>> print(left_rotation(5,1,[1,2,3,4,5]))
1
2
3
4
5
[2, 3, 4, 5, 1]

Upvotes: 4

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