arrays,algorithm,select , Selection algorithm from an array of square with radius?


Selection algorithm from an array of square with radius?

Question:

Tag: arrays,algorithm,select

As is an algorithm which selects the elements of the array at a predetermined radius from the support element?

For example I select item 28 (see the picture), radius = 1 selected :

19 20 21 
27 28 29
35 36 37

if support element is 1 radius = 1 selected:

1 2
9 10

The algorithm is to take 28 item check whether the elements above to take it (20), check whether there is a higher take it (12), followed by 20 and 12 check and take the right elements within a radius of 2, rotated 90 degrees and repeat.

That for the algorithm or what it looks like ?

Visualization of the algorithm: http://i.stack.imgur.com/Cy0Uu.jpg


Answer:

If your selected element is at (row, col), it looks like a simple matter of traversing the submatrix with (row, col) at its center.

We must take care to avoid out of bounds issues.

Pseudocode:

for rowIndex = max(0, row - radius) to min(matrixHeight - 1, row + radius)
  for colIndex = max(0, col - radius) to min(matrixWidth - 1, col + radius)
    take element at (rowIndex, colIndex)

If you also want to color the elements like in your image, then this is easily done by comparing the position (rowIndex, colIndex) with that of (row, col): for example, if rowIndex > row and colIndex >= colIndex, then color that element red.


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