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This article is about how to realize the rotation matrix of two-dimensional array in LeetCode. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Topic description: "the matrix of clothing Numbn represents the image, in which the size of each pixel is 4 bytes. Design an algorithm to rotate the image 90 degrees."

Example:

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

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

The first attempt

By observing the law of array rotation, we can create a new two-dimensional array and use a loop to input data elements into the new two-dimensional array according to the law of rotation.

Note: when range (start, stop,-1) traverses from large to small, it only takes the subscript position of stop+1.

Although this method solves the problem, it takes up extra memory (creates a new two-dimensional array)

Algorithm optimization-does not occupy extra memory

If you don't occupy memory, you can't create a new variable, but change it on the original array.

The rotation of the matrix has a special rule:

First exchange the diagonal elements of the matrix

Arrange each row (one-dimensional array) in reverse order

Note:

Python variable exchange syntax:

Matrix [I] [j], matrix [j] [I] = matrix [j] [I], matrix [I] [j]

When traversing the two-tier loop, note that the second-tier loop does not start at 0, otherwise each situation will repeat and eventually return to the origin. Instead, it starts traversing from the I of the previous loop. The last exchange in the diagonal exchange element is that the element in the lower right corner swaps with itself, and there is only one exchange. If you start at 0, then every I has three swaps.

For i in range (len (matrix [0])): for j in range (I, len (matrix)): thank you for reading! This is the end of the article on "how to achieve rotation matrix in two-dimensional array in LeetCode". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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