通过切片向右旋转数组

Question

I am trying to do an in-place right rotation of an array nums k times. I can't get my head around why my code works for one array and fails for another.

Code - nums[:]=nums[-k:]+nums[:k+1]

Works for nums=[1,2,3,4,5,6,7] and k=3

Output - nums=[5, 6, 7, 1, 2, 3, 4]

Fails for nums=[-1,-100,3,99] k=2

Output - [3, 99, -1, -100, 3] Desired Output - [3, 99, -1, -100]

Answer 1

I found a solution in https://www.geeksforgeeks.org/python-ways-to-rotate-a-list/

It says you can rotate right by doing

nums=[-1,-100,3,99]
k = 2
nums = nums[-k:] + nums[:-k]
print(nums)

The output is [3, 99, -1, -100]

Explanation: First, you take the desired ( k ) number of elements from the right side of the list and place them as the start of the rotated list ( nums[-k:] ). Second, you take the left side of the list and place it at the end of the new list ( nums[:-k] ). This will not work if k > len(nums) .

Answer 2

both outputs are logical.

#nums[-k:] is [3,99]
#nums[:k+1] is [-1,-100,3]
#Output is [3, 99, -1, -100,3]

i think your solution isn't optimal i think this might help you: [1]: https://www.techiedelight.com/right-rotate-an-array-k-times/

Answer 3

PHP solution:

slice array into 2 parts and merge in reverse order.

$c = count($A);
    $a1 = array_splice($A,0,$c - $K );
    $a2 = $A;
    return array_merge($a2,$a1);