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<a name="L1"></a><span id="L1" class="LineNr"> 1 </span><span class="Comment"># <a href="http://rosettacode.org/wiki/N-queens_problem">http://rosettacode.org/wiki/N-queens_problem</a></span>
<a name="L2"></a><span id="L2" class="LineNr"> 2 </span><span class="Comment"># port of the Arc solution at <a href="http://arclanguage.org/item?id=19743">http://arclanguage.org/item?id=19743</a></span>
<a name="L3"></a><span id="L3" class="LineNr"> 3 </span><span class="Comment"># run with tracing turned on:</span>
<a name="L4"></a><span id="L4" class="LineNr"> 4 </span><span class="Comment"># ./mu --trace nqueens.mu</span>
<a name="L5"></a><span id="L5" class="LineNr"> 5 </span>
<a name="L6"></a><span id="L6" class="LineNr"> 6 </span><span class="muData">container</span> square [
<a name="L7"></a><span id="L7" class="LineNr"> 7 </span> rank:num
<a name="L8"></a><span id="L8" class="LineNr"> 8 </span> file:num
<a name="L9"></a><span id="L9" class="LineNr"> 9 </span>]
<a name="L10"></a><span id="L10" class="LineNr">10 </span>
<a name="L11"></a><span id="L11" class="LineNr">11 </span><span class="muRecipe">def</span> nqueens n:num, queens:&:list:square<span class="muRecipe"> -> </span>result:num, queens:&:list:square [
<a name="L12"></a><span id="L12" class="LineNr">12 </span> <span class="Constant">local-scope</span>
<a name="L13"></a><span id="L13" class="LineNr">13 </span> <span class="Constant">load-ingredients</span>
<a name="L14"></a><span id="L14" class="LineNr">14 </span> <span class="Comment"># if 'queens' is already long enough, print it and return</span>
<a name="L15"></a><span id="L15" class="LineNr">15 </span> added-so-far:num <span class="Special"><-</span> length queens
<a name="L16"></a><span id="L16" class="LineNr">16 </span> <span class="Delimiter">{</span>
<a name="L17"></a><span id="L17" class="LineNr">17 </span> done?:bool <span class="Special"><-</span> greater-or-equal added-so-far, n
<a name="L18"></a><span id="L18" class="LineNr">18 </span> <span class="muControl">break-unless</span> done?
<a name="L19"></a><span id="L19" class="LineNr">19 </span> stash queens
<a name="L20"></a><span id="L20" class="LineNr">20 </span> <span class="muControl">return</span><span class="Constant"> 1</span>
<a name="L21"></a><span id="L21" class="LineNr">21 </span> <span class="Delimiter">}</span>
<a name="L22"></a><span id="L22" class="LineNr">22 </span> <span class="Comment"># still work to do</span>
<a name="L23"></a><span id="L23" class="LineNr">23 </span> next-rank:num <span class="Special"><-</span> copy<span class="Constant"> 0</span>
<a name="L24"></a><span id="L24" class="LineNr">24 </span> <span class="Delimiter">{</span>
<a name="L25"></a><span id="L25" class="LineNr">25 </span> <span class="muControl">break-unless</span> queens
<a name="L26"></a><span id="L26" class="LineNr">26 </span> first:square <span class="Special"><-</span> first queens
<a name="L27"></a><span id="L27" class="LineNr">27 </span> existing-rank:num <span class="Special"><-</span> get first, <span class="Constant">rank:offset</span>
<a name="L28"></a><span id="L28" class="LineNr">28 </span> next-rank <span class="Special"><-</span> add existing-rank,<span class="Constant"> 1</span>
<a name="L29"></a><span id="L29" class="LineNr">29 </span> <span class="Delimiter">}</span>
<a name="L30"></a><span id="L30" class="LineNr">30 </span> result <span class="Special"><-</span> copy<span class="Constant"> 0</span>
<a name="L31"></a><span id="L31" class="LineNr">31 </span> next-file:num <span class="Special"><-</span> copy<span class="Constant"> 0</span>
<a name="L32"></a><span id="L32" class="LineNr">32 </span> <span class="Delimiter">{</span>
<a name="L33"></a><span id="L33" class="LineNr">33 </span> done?:bool <span class="Special"><-</span> greater-or-equal next-file, n
<a name="L34"></a><span id="L34" class="LineNr">34 </span> <span class="muControl">break-if</span> done?
<a name="L35"></a><span id="L35" class="LineNr">35 </span> curr:square <span class="Special"><-</span> merge next-rank, next-file
<a name="L36"></a><span id="L36" class="LineNr">36 </span> <span class="Delimiter">{</span>
<a name="L37"></a><span id="L37" class="LineNr">37 </span> curr-conflicts?:bool <span class="Special"><-</span> conflict? curr, queens
<a name="L38"></a><span id="L38" class="LineNr">38 </span> <span class="muControl">break-if</span> curr-conflicts?
<a name="L39"></a><span id="L39" class="LineNr">39 </span> queens:&:list:square <span class="Special"><-</span> push curr, queens
<a name="L40"></a><span id="L40" class="LineNr">40 </span> sub-result:num <span class="Special"><-</span> nqueens n, queens
<a name="L41"></a><span id="L41" class="LineNr">41 </span> result <span class="Special"><-</span> add result, sub-result
<a name="L42"></a><span id="L42" class="LineNr">42 </span> queens <span class="Special"><-</span> rest queens
<a name="L43"></a><span id="L43" class="LineNr">43 </span> <span class="Delimiter">}</span>
<a name="L44"></a><span id="L44" class="LineNr">44 </span> next-file <span class="Special"><-</span> add next-file,<span class="Constant"> 1</span>
<a name="L45"></a><span id="L45" class="LineNr">45 </span> <span class="muControl">loop</span>
<a name="L46"></a><span id="L46" class="LineNr">46 </span> <span class="Delimiter">}</span>
<a name="L47"></a><span id="L47" class="LineNr">47 </span>]
<a name="L48"></a><span id="L48" class="LineNr">48 </span>
<a name="L49"></a><span id="L49" class="LineNr">49 </span><span class="muRecipe">def</span> conflict? curr:square, queens:&:list:square<span class="muRecipe"> -> </span>result:bool [
<a name="L50"></a><span id="L50" class="LineNr">50 </span> <span class="Constant">local-scope</span>
<a name="L51"></a><span id="L51" class="LineNr">51 </span> <span class="Constant">load-ingredients</span>
<a name="L52"></a><span id="L52" class="LineNr">52 </span> result1:bool <span class="Special"><-</span> conflicting-file? curr, queens
<a name="L53"></a><span id="L53" class="LineNr">53 </span> <span class="muControl">return-if</span> result1, result1
<a name="L54"></a><span id="L54" class="LineNr">54 </span> result2:bool <span class="Special"><-</span> conflicting-diagonal? curr, queens
<a name="L55"></a><span id="L55" class="LineNr">55 </span> <span class="muControl">return</span> result2
<a name="L56"></a><span id="L56" class="LineNr">56 </span>]
<a name="L57"></a><span id="L57" class="LineNr">57 </span>
<a name="L58"></a><span id="L58" class="LineNr">58 </span><span class="muRecipe">def</span> conflicting-file? curr:square, queens:&:list:square<span class="muRecipe"> -> </span>result:bool [
<a name="L59"></a><span id="L59" class="LineNr">59 </span> <span class="Constant">local-scope</span>
<a name="L60"></a><span id="L60" class="LineNr">60 </span> <span class="Constant">load-ingredients</span>
<a name="L61"></a><span id="L61" class="LineNr">61 </span> curr-file:num <span class="Special"><-</span> get curr, <span class="Constant">file:offset</span>
<a name="L62"></a><span id="L62" class="LineNr">62 </span> <span class="Delimiter">{</span>
<a name="L63"></a><span id="L63" class="LineNr">63 </span> <span class="muControl">break-unless</span> queens
<a name="L64"></a><span id="L64" class="LineNr">64 </span> q:square <span class="Special"><-</span> first queens
<a name="L65"></a><span id="L65" class="LineNr">65 </span> qfile:num <span class="Special"><-</span> get q, <span class="Constant">file:offset</span>
<a name="L66"></a><span id="L66" class="LineNr">66 </span> file-match?:bool <span class="Special"><-</span> equal curr-file, qfile
<a name="L67"></a><span id="L67" class="LineNr">67 </span> <span class="muControl">return-if</span> file-match?, <span class="Constant">1/conflict-found</span>
<a name="L68"></a><span id="L68" class="LineNr">68 </span> queens <span class="Special"><-</span> rest queens
<a name="L69"></a><span id="L69" class="LineNr">69 </span> <span class="muControl">loop</span>
<a name="L70"></a><span id="L70" class="LineNr">70 </span> <span class="Delimiter">}</span>
<a name="L71"></a><span id="L71" class="LineNr">71 </span> <span class="muControl">return</span> <span class="Constant">0/no-conflict-found</span>
<a name="L72"></a><span id="L72" class="LineNr">72 </span>]
<a name="L73"></a><span id="L73" class="LineNr">73 </span>
<a name="L74"></a><span id="L74" class="LineNr">74 </span><span class="muRecipe">def</span> conflicting-diagonal? curr:square, queens:&:list:square<span class="muRecipe"> -> </span>result:bool [
<a name="L75"></a><span id="L75" class="LineNr">75 </span> <span class="Constant">local-scope</span>
<a name="L76"></a><span id="L76" class="LineNr">76 </span> <span class="Constant">load-ingredients</span>
<a name="L77"></a><span id="L77" class="LineNr">77 </span> curr-rank:num <span class="Special"><-</span> get curr, <span class="Constant">rank:offset</span>
<a name="L78"></a><span id="L78" class="LineNr">78 </span> curr-file:num <span class="Special"><-</span> get curr, <span class="Constant">file:offset</span>
<a name="L79"></a><span id="L79" class="LineNr">79 </span> <span class="Delimiter">{</span>
<a name="L80"></a><span id="L80" class="LineNr">80 </span> <span class="muControl">break-unless</span> queens
<a name="L81"></a><span id="L81" class="LineNr">81 </span> q:square <span class="Special"><-</span> first queens
<a name="L82"></a><span id="L82" class="LineNr">82 </span> qrank:num <span class="Special"><-</span> get q, <span class="Constant">rank:offset</span>
<a name="L83"></a><span id="L83" class="LineNr">83 </span> qfile:num <span class="Special"><-</span> get q, <span class="Constant">file:offset</span>
<a name="L84"></a><span id="L84" class="LineNr">84 </span> rank-delta:num <span class="Special"><-</span> subtract qrank, curr-rank
<a name="L85"></a><span id="L85" class="LineNr">85 </span> file-delta:num <span class="Special"><-</span> subtract qfile, curr-file
<a name="L86"></a><span id="L86" class="LineNr">86 </span> rank-delta <span class="Special"><-</span> abs rank-delta
<a name="L87"></a><span id="L87" class="LineNr">87 </span> file-delta <span class="Special"><-</span> abs file-delta
<a name="L88"></a><span id="L88" class="LineNr">88 </span> diagonal-match?:bool <span class="Special"><-</span> equal rank-delta, file-delta
<a name="L89"></a><span id="L89" class="LineNr">89 </span> <span class="muControl">return-if</span> diagonal-match?, <span class="Constant">1/conflict-found</span>
<a name="L90"></a><span id="L90" class="LineNr">90 </span> queens <span class="Special"><-</span> rest queens
<a name="L91"></a><span id="L91" class="LineNr">91 </span> <span class="muControl">loop</span>
<a name="L92"></a><span id="L92" class="LineNr">92 </span> <span class="Delimiter">}</span>
<a name="L93"></a><span id="L93" class="LineNr">93 </span> <span class="muControl">return</span> <span class="Constant">0/no-conflict-found</span>
<a name="L94"></a><span id="L94" class="LineNr">94 </span>]
<a name="L95"></a><span id="L95" class="LineNr">95 </span>
<a name="L96"></a><span id="L96" class="LineNr">96 </span><span class="muRecipe">def</span> main [
<a name="L97"></a><span id="L97" class="LineNr">97 </span> nqueens<span class="Constant"> 4</span>
<a name="L98"></a><span id="L98" class="LineNr">98 </span> $dump-trace <span class="Constant">[app]</span>
<a name="L99"></a><span id="L99" class="LineNr">99 </span>]
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