[Leetcode] Matrix

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48. Rotate Image

Matrix Rotation Problems
Solution Template

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/*
 * clockwise rotate
 * first reverse up to down, then swap the symmetry 
 * 1 2 3     7 8 9     7 4 1
 * 4 5 6  => 4 5 6  => 8 5 2
 * 7 8 9     1 2 3     9 6 3
*/

/*
 * anticlockwise rotate
 * first reverse left to right, then swap the symmetry
 * 1 2 3     3 2 1     3 6 9
 * 4 5 6  => 6 5 4  => 2 5 8
 * 7 8 9     9 8 7     1 4 7
*/
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def rotate(self, matrix: 'List[List[int]]') -> 'None':
    if not matrix or len(matrix) == 0 or len(matrix[0]) == 0:
        return
    matrix.reverse()
    n = len(matrix)
    cnt = 0
    for i in range(len(matrix)):
        j = i
        while j < len(matrix):
            temp = matrix[i][j]
            matrix[i][j] = matrix[j][i]
            matrix[j][i] = temp
            j += 1