CodeSignal-Arrays(3):rotateImage

Question

Note: Try to solve this task in-place (with O(1) additional memory), since this is what you'll be asked to do during an interview.

You are given an n x n 2D matrix that represents an image. Rotate the image by 90 degrees (clockwise).

Example

For

a = [[1, 2, 3],
     [4, 5, 6],
     [7, 8, 9]]

the output should be

solution(a) =
    [[7, 4, 1],
     [8, 5, 2],
     [9, 6, 3]]

Input/Output

• [execution time limit] 4 seconds (py3)

• [memory limit] 1 GB

• [input] array.array.integer a

  Guaranteed constraints:
  1 ≤ a.length ≤ 100,
  a[i].length = a.length,
  1 ≤ a[i][j] ≤ 104.

• [output] array.array.integer

Answer python

def solution(a):
    n = len(a)
    for layer in range(n // 2):
        for i in range(layer, n - layer - 1):
            temp = a[layer][i]
            a[layer][i] = a[n - i - 1][layer]
            a[n - i - 1][layer] = a[n - layer - 1][n - i - 1]
            a[n - layer - 1][n - i - 1] = a[i][n - layer - 1]
            a[i][n - layer - 1] = temp
    return a