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fix(formatting): Zhang-Suen | Rosetta Code (#35472)

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* fix(formatting): Move challenge instructions to instruction section

* Fix table and list

* fix(curriculum): Zhangsuen

* fix(curriculum): add bold tags

* Fix typo in instructions
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The Coding Aviator 2019-03-18 13:49:02 +05:30 committed by Kristofer Koishigawa
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curriculum/challenges/english/08-coding-interview-prep/rosetta-code/zhang-suen-thinning-algorithm.english.md
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@ -25,7 +25,7 @@ For example, with an input image of:
######## ####### ###### ################## ######
######## ####### ###### ################ ######
######## ####### ###### ############# ######
</pre>
</pre>
It produces the thinned output:
<pre>
@ -44,49 +44,52 @@ It produces the thinned output:
# ############
### ###
</pre>
</pre>
<h2>Algorithm</h2>
Assume black pixels are one and white pixels zero, and that the input image is a rectangular N by M array of ones and zeroes.
The algorithm operates on all black pixels P1 that can have eight neighbours. The neighbours are, in order, arranged as:
<table border="1">
<tr><td>P9</td><td>P2</td><td>P3</td></tr>
<tr><td>P8</td><td><b>P1</b></td><td>P4</td></tr>
<tr><td>P7</td><td>P6</td><td>P5</td></tr>
<table border="3">
<tr><td style="text-align: center;">P9</td><td style="text-align: center;">P2</td><td style="text-align: center;">P3</td></tr>
<tr><td style="text-align: center;">P8</td><td style="text-align: center;"><b>P1</b></td><td style="text-align: center;">P4</td></tr>
<tr><td style="text-align: center;">P7</td><td style="text-align: center;">P6</td><td style="text-align: center;">P5</td></tr>
</table>
Obviously the boundary pixels of the image cannot have the full eight neighbours.
Define $A(P1)$ = the number of transitions from white to black, (0 -> 1) in the sequence P2,P3,P4,P5,P6,P7,P8,P9,P2. (Note the extra P2 at the end - it is circular).
Define $B(P1)$ = the number of black pixel neighbours of P1. ( = sum(P2 .. P9) )
<ul>
<li>Define $A(P1)$ = the number of transitions from white to black, (0 -> 1) in the sequence P2, P3, P4, P5, P6, P7, P8, P9, P2. (Note the extra P2 at the end - it is circular).</li>
<li>Define $B(P1)$ = the number of black pixel neighbours of P1. ( = sum(P2 .. P9) )</li>
</ul>
<h3>Step 1:</h3>
All pixels are tested and pixels satisfying all the following conditions (simultaneously) are just noted at this stage.
(0) The pixel is black and has eight neighbours
(1) $2 <= B(P1) <= 6$
(2) $A(P1) = 1$
(3) At least one of P2 and P4 and P6 is white
(4) At least one of P4 and P6 and P8 is white
<ol>
<li>The pixel is black and has eight neighbours</li>
<li>$2 <= B(P1) <= 6$</li>
<li>$A(P1) = 1$</li>
<li>At least one of <b>P2, P4 and P6</b> is white</li>
<li>At least one of <b>P4, P6 and P8</b> is white</li>
</ol>
After iterating over the image and collecting all the pixels satisfying all step 1 conditions, all these condition satisfying pixels are set to white.
<h3>Step 2:</h3>
All pixels are again tested and pixels satisfying all the following conditions are just noted at this stage.
(0) The pixel is black and has eight neighbours
(1) $2 <= B(P1) <= 6$
(2) $A(P1) = 1$
(3) At least one of P2 and P4 and '''P8''' is white
(4) At least one of '''P2''' and P6 and P8 is white
<ol>
<li>The pixel is black and has eight neighbours</li>
<li>$2 <= B(P1) <= 6$</li>
<li>$A(P1) = 1$</li>
<li>At least one of <b>P2, P4 and P8</b> is white</li>
<li>At least one of <b>P2, P6 and P8</b> is white</li>
</ol>
After iterating over the image and collecting all the pixels satisfying all step 2 conditions, all these condition satisfying pixels are again set to white.
Iteration:
<h3>Iteration:</h3>
If any pixels were set in this round of either step 1 or step 2 then all steps are repeated until no image pixels are so changed.
<p>
Task:
Write a routine to perform Zhang-Suen thinning on an image matrix of ones and zeroes.
</p>
</section>
## Instructions
<section id='instructions'>
Write a routine to perform Zhang-Suen thinning on the provided image matrix.
</section>
## Tests