Cracking the Coding Interview-1.7

第六版Cracking the Coding Interview题目1.7，题目如下：

Rotate Matrix: Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

题目是顺时针90度旋转矩阵，若使用numpy可直接调用numpy.rot90(matrix,3)，若不使用numpy，则直接按要求调换元素位置如下：

def rotatemMatrix(matrix):
    n = len(matrix)
    for layer in xrange(n / 2):
        first, last = layer, n - layer - 1
        for i in xrange(first, last):
            # save top
            top = matrix[layer][i]
            # left -> top
            matrix[layer][i] = matrix[-i - 1][layer]
            # bottom -> left
            matrix[-i - 1][layer] = matrix[-layer - 1][-i - 1]
            # right -> bottom
            matrix[-layer - 1][-i - 1] = matrix[i][- layer - 1]
            # top -> right
            matrix[i][- layer - 1] = top
    return matrix

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Cracking the Coding Interview-1.7

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