68 lines
1.2 KiB
Markdown
68 lines
1.2 KiB
Markdown
---
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layout: page
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title: Rotate Matrix
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last_solved: 2020-06-10
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category: Matrix
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leetcode_url: https://leetcode.com/problems/rotate-image/
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status: Solved
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---
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Problem
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-------
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```
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Given input matrix =
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[
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[1,2,3],
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[4,5,6],
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[7,8,9]
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],
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rotate the input matrix in-place such that it becomes:
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[
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[7,4,1],
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[8,5,2],
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[9,6,3]
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]
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```
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Solution
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----------
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Transpose and Flip. This is the second time that I'm seeing this and I really worked hard to understand it the first time.
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The second time, I was able to:
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- recall "the solution"
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- code up the solution and get the array indexes and loop ranges correct (things I usually mess up on)
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{% highlight python %}
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def rotateMatrix(mat):
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N = len(mat)
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# transpose
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for i in range(N):
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for j in range(i, N):
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tmp = mat[i][j]
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mat[i][j] = mat[j][i]
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mat[j][i] = tmp
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print( 'after transpose: ', mat )
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# flip horizontally
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for i in range(N):
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for j in range(N//2):
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# swap j and N-j
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tmp = mat[i][j]
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mat[i][j] = mat[i][N-j-1]
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mat[i][N-j-1] = tmp
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print( 'after flip: ', mat )
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{% endhighlight %}
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![image1]() |