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POCode Golf: Zigzag pattern scanning
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copied!<h2>The Challenge</h2> <p>The shortest code by character count that takes a single input integer <code>N</code> (N >= 3) and returns an array of indices that when iterated would traverse an <code>N</code>x<code>N</code> matrix according to the JPEG "zigzag" scan pattern. The following is an example traversal over an 8x8 matrix<sup><a href="http://en.wikipedia.org/wiki/Jpeg" rel="nofollow noreferrer">src</a></sup>:</p> <p><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/4/43/JPEG_ZigZag.svg/220px-JPEG_ZigZag.svg.png" alt="zigzag layout pattern"></p> <h3>Examples</h3> <p>(The middle matrix is not part of the input or output, just a representation of the NxN matrix the input represents.)</p> <pre><code> 1 2 3 (Input) 3 --> 4 5 6 --> 1 2 4 7 5 3 6 8 9 (Output) 7 8 9 1 2 3 4 (Input) 4 --> 5 6 7 8 --> 1 2 5 9 6 3 4 7 10 13 14 11 8 12 15 16 (Output) 9 10 11 12 13 14 15 16 </code></pre> <h3>Notes</h3> <ul> <li>The resulting array's base should be appropriate for your language (e.g., Matlab arrays are 1-based, C++ arrays are 0-based).</li> <li>This is related to <a href="https://stackoverflow.com/questions/3024939">this question</a>.</li> </ul> <h2>Bonus</h2> <p>Extend your answer to take two inputs <code>N</code> and <code>M</code> (N, M >=3) and perform the same scan over an <code>N</code>x<code>M</code> matrix. (In this case <code>N</code> would be the number of columns and <code>M</code> the number of rows.)</p> <h3>Bonus Examples</h3> <pre><code> 1 2 3 4 (Input) 4 3 --> 5 6 7 8 --> 1 2 5 9 6 3 4 7 10 11 8 12 (Output) 9 10 11 12 1 2 3 (Input) 3 4 --> 4 5 6 --> 1 2 4 7 5 3 6 8 10 11 9 12 (Output) 7 8 9 10 11 12 </code></pre>

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