73 lines
5.5 KiB
Markdown
73 lines
5.5 KiB
Markdown
---
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title: Ninety-nine Lisp Problems – P10の解答
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author: kazu634
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date: 2010-11-24
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wordtwit_post_info:
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categories:
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- gauche
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- Lisp
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---
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<div class="section">
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<p>
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P9の解答で作成した関数を元にして、リスト空リストへの変換を行う形で解答を作成してみました。つまり
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</p>
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<ol>
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<li>
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packでリストを作成する
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</li>
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<li>
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packで作られたリストの中のリストを変換する手続きencode-listを作成する
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</li>
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<li>
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packに対してencode-listをmapする
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</li>
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</ol>
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<p>
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感じでやってみました。
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</p>
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<h4>
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ソース
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</h4>
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<pre class="syntax-highlight">
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<span class="synComment">;; P10 (*) Run-length encoding of a list.</span>
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<span class="synComment">;; Use the result of problem P09 to implement the so-called run-length encoding data compression method. Consecutive duplicates of elements are encoded as lists (N E) where N is the number of duplicates of the element E.</span>
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<span class="synComment">;; Example:</span>
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<span class="synComment">;; * (encode '(a a a a b c c a a d e e e e))</span>
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<span class="synComment">;; ((4 A) (1 B) (2 C) (2 A) (1 D)(4 E))</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>pack-seed front sublist result l<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">cond</span>
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[<span class="synSpecial">(</span><span class="synStatement">null</span>? l<span class="synSpecial">)</span> <span class="synSpecial">(</span><span class="synStatement">append</span> result <span class="synSpecial">(</span><span class="synStatement">list</span> sublist<span class="synSpecial">))</span>]
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[<span class="synSpecial">(</span><span class="synStatement">eq</span>? front <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">))</span> <span class="synSpecial">(</span>pack-seed front
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<span class="synSpecial">(</span><span class="synStatement">append</span> sublist
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<span class="synSpecial">(</span><span class="synStatement">list</span> front<span class="synSpecial">))</span>
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result
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<span class="synSpecial">(</span><span class="synStatement">cdr</span> l<span class="synSpecial">))</span>]
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[else <span class="synSpecial">(</span>pack-seed <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">))</span>
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<span class="synSpecial">(</span><span class="synStatement">if</span> <span class="synSpecial">(</span><span class="synStatement">null</span>? result<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">if</span> <span class="synSpecial">(</span><span class="synStatement">null</span>? sublist<span class="synSpecial">)</span>
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<span class="synSpecial">'()</span>
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<span class="synSpecial">(</span><span class="synStatement">append</span> result <span class="synSpecial">(</span><span class="synStatement">list</span> sublist<span class="synSpecial">)))</span>
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<span class="synSpecial">(</span><span class="synStatement">append</span> result <span class="synSpecial">(</span><span class="synStatement">list</span> sublist<span class="synSpecial">)))</span>
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<span class="synSpecial">(</span><span class="synStatement">cdr</span> l<span class="synSpecial">))</span>]<span class="synSpecial">))</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>pack l<span class="synSpecial">)</span>
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<span class="synSpecial">(</span>pack-seed #f <span class="synSpecial">'()</span> <span class="synSpecial">'()</span> l<span class="synSpecial">))</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>encode-list l<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">let</span> <span class="synSpecial">((</span>num <span class="synSpecial">(</span><span class="synStatement">length</span> l<span class="synSpecial">)))</span>
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<span class="synSpecial">(</span><span class="synStatement">append</span> <span class="synSpecial">(</span><span class="synStatement">list</span> num<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">list</span> <span class="synSpecial">(</span><span class="synStatement">car</span> l<span class="synSpecial">)))))</span>
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<span class="synSpecial">(</span>encode-list <span class="synSpecial">'(</span>a a a a a<span class="synSpecial">))</span>
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<span class="synSpecial">(</span>define <span class="synSpecial">(</span>encode l<span class="synSpecial">)</span>
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<span class="synSpecial">(</span><span class="synStatement">map</span> <span class="synSpecial">(</span><span class="synStatement">lambda</span> <span class="synSpecial">(</span>l<span class="synSpecial">)</span>
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<span class="synSpecial">(</span>encode-list l<span class="synSpecial">))</span>
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<span class="synSpecial">(</span>pack l<span class="synSpecial">)))</span>
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<span class="synSpecial">(</span>encode <span class="synSpecial">'(</span>a a a a b c c a a d e e e e<span class="synSpecial">))</span>
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</pre>
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</div>
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