尝试将矩阵旋转 90 度但无法正常工作

Question

def rotate_ninety(matrix):
    putin = []
    temporary = []
    row_size = len(matrix)
    col_size = len(matrix[0])
    ccount = col_size-1
    putin_idx = 0
    while ccount > -1:
        for i in range(row_size):
            temporary.insert(i, matrix[i][ccount])

        putin.insert(putin_idx, temporary)
        ccount = ccount -1
        temporary.clear()
        putin_idx += 1

    print(putin)
    return 0

So, if I had the input

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

The result should be:

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

However, when I print putin I get [[] [] []], an array of all empty things, which I don't understand where my logic went wrong. I know there are other more efficient ways to do this, but I don't see how my code is wrong

Answer 1

When you assign (append or insert) a list to a variable (another list), the list object will be assigned or appended. Since after you add the temporary list to the putin list and then clearing the temporary , the object that has been added just got removed,too. You need to add a copy of the temporary list to the putin , like this:

import copy

def rotate_ninety(matrix):
    putin = []
    temporary = []
    row_size = len(matrix)
    col_size = len(matrix[0])
    ccount = col_size-1
    putin_idx = 0
    while ccount > -1:
        for i in range(row_size):
            temporary.append(matrix[i][ccount])
        putin.append(copy.copy(temporary))
        ccount = ccount -1
        temporary.clear()
        putin_idx += 1

    print(putin)
    return 0

matrix = [[1,2,3],[4,5,6],[7,8,9]]
rotate_ninety(matrix)

And the result will be:
[[3, 6, 9], [2, 5, 8], [1, 4, 7]]

Answer 2

Here's a simply way with numpy:

matrix = np.arange(1,10).reshape((3,3))

rotated_90 = matrix.T[::-1]