blocks|key|909434|text|R，62字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|909435|function(n){while(sum(F%7C1)<n)F=c(match(F[1],F[-1],0),F)
%2BF[1]}|code-block|syntax|javascript|909436|在网上试试！|unstyled|909437|反向构建列表；match返回F[-1]中的F[1]的第一个索引(前一个值)(列表的其余部分)，如果没有找到匹配项，则返回0。|style|CODE|909438|F被初始化为FALSE，并在while循环的第一次传递时被强制为0。|entityMap|0|LINK|mutability|MUTABLE|url|https://www.r-project.org/|1|https://tio.run/##K/qfpmCj@z@tNC@5JDM/TyNPs7o8IzMnVaO4NFfDrcZQ0yZP0802WSM3sSQ5Q8Mt2jBWxy1aF0gaaOq4aXJpg0Rq/xcnFhTkVGoYWhka6KRp/gcA^0|0|1|0|0|0|0|6|1|0|7|5|E|5|L|4|1O|1|0|0|1|6|5|E|5|W|1^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|L|3|M|5|K|7|19|8|@$A|1A|B|1B|N|O]|$A|1C|B|1D|N|O]|$A|1E|B|1F|N|O]|$A|1G|B|1H|N|O]]|9|@]|C|$]]|$1|P|3|Q|5|K|7|1I|8|@$A|1J|B|1K|N|O]|$A|1L|B|1M|N|O]|$A|1N|B|1O|N|O]|$A|1P|B|1Q|N|O]]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

<h1><a href="https://www.r-project.org/" rel="noreferrer">R</a>, 62 bytes</h1>



<pre class="lang-r prettyprint-override"><code>function(n){while(sum(F|1)&lt;n)F=c(match(F[1],F[-1],0),F)
+F[1]}
</code></pre>

<p><a href="https://tio.run/##K/qfpmCj@z@tNC@5JDM/TyNPs7o8IzMnVaO4NFfDrcZQ0yZP0802WSM3sSQ5Q8Mt2jBWxy1aF0gaaOq4aXJpg0Rq/xcnFhTkVGoYWhka6KRp/gcA" rel="noreferrer" title="R – Try It Online">Try it online!</a></p>

<p>Builds the list in reverse; <code>match</code> returns the <em>first</em> index of <code>F[1]</code> (the previous value) in <code>F[-1]</code> (the remainder of the list), returning <code>0</code> if no match is found.</p>

<p><code>F</code> is initialized to <code>FALSE</code> and is coerced to <code>0</code> on the first pass of the <code>while</code> loop.</p>


blocks|key|904139|text|Python，51字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|904140|f=lambda+n,i=1:n>i+and[f(n,i%2B1),i][f(n-1)==f(n%2B~i)]|code-block|syntax|javascript|904141|在网上试试！|unstyled|904142|输出False用于0。按字面意思实现规范，寻找最低的正整数i，例如f(n-1)==f(n-i-1)。如果这样的搜索导致了i>=n，那么前面的元素以前就没有出现过，所以我们生成了0。|style|CODE|904143|函数没有做一些合理的事情，比如将早期的值存储在列表中，而是在需要时从零开始递归地重新计算它们，有时是在不需要它们的时候。这使得该函数对于10以上的输入运行得非常慢。|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/2/|1|https://tio.run/##K6gsycjPM/r/P802JzE3KSVRIU8n09bQKs8uUyExLyU6TQPI1zbU1MmMBbF1DTVtbYG0dl2mZuz/tPwihTyFzDyFosS89FQNQ0NNKy6FgqLMvBKgKQraQHWa/wE^0|0|6|0|0|0|0|6|1|0|2|5|9|1|T|1|X|G|1O|4|2G|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|L|3|M|5|K|7|19|8|@$A|1A|B|1B|N|O]|$A|1C|B|1D|N|O]|$A|1E|B|1F|N|O]|$A|1G|B|1H|N|O]|$A|1I|B|1J|N|O]|$A|1K|B|1L|N|O]]|9|@]|C|$]]|$1|P|3|Q|5|K|7|1M|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

<h1><a href="https://docs.python.org/2/" rel="noreferrer">Python</a>, 51 bytes</h1>



<pre class="lang-python prettyprint-override"><code>f=lambda n,i=1:n&gt;i and[f(n,i+1),i][f(n-1)==f(n+~i)]
</code></pre>

<p><a href="https://tio.run/##K6gsycjPM/r/P802JzE3KSVRIU8n09bQKs8uUyExLyU6TQPI1zbU1MmMBbF1DTVtbYG0dl2mZuz/tPwihTyFzDyFosS89FQNQ0NNKy6FgqLMvBKgKQraQHWa/wE" rel="noreferrer" title="Python 2 – Try It Online">Try it online!</a></p>

<p>Outputs <code>False</code> for <code>0</code>. Implements the spec pretty literally, looking for the lowest positive integer <code>i</code> such that <code>f(n-1)==f(n-i-1)</code>. If such a search leads to <code>i&gt;=n</code>, the previous element hasn't appeared before and we produce <code>0</code>.</p>

<p>Instead of doing something reasonable like storing earlier values in a list, the function just recomputes them recursively from scratch whenever they're needed, and sometimes when they're not needed. This makes the function run very slowly for inputs above 10 or so.</p>


blocks|key|903895|text|Wolfram语言(数学)，48字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|903896|#<1%7C%7CLast[#-1-Array[#0,#-2]~Position~#0[#-1],0]&|code-block|syntax|javascript|903897|在网上试试！|unstyled|903898|非零值是作为单例列表返回。|entityMap|0|LINK|mutability|MUTABLE|url|https://www.wolfram.com/wolframscript/|1|https://tio.run/##y00syUjNTSzJTE78n2b7X9nGsKbGJ7G4JFpZ11DXsagosTJa2UBHWdcoti4gvzizJDM/r07ZACQbq2MQq/Y/sDQztSQ6oCgzD6TFLs1BOVZN3yEoMS891cHQIPY/AA|2|https://codegolf.meta.stackexchange.com/a/11884/81203^0|0|D|0|0|0|0|6|1|0|4|8|2^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|L|3|M|5|K|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]|W|$5|P|Q|R|C|$S|X]]]]

<h1><a href="https://www.wolfram.com/wolframscript/" rel="noreferrer">Wolfram Language (Mathematica)</a>, 48 bytes</h1>

<pre><code>#&lt;1||Last[#-1-Array[#0,#-2]~Position~#0[#-1],0]&amp;
</code></pre>

<p><a href="https://tio.run/##y00syUjNTSzJTE78n2b7X9nGsKbGJ7G4JFpZ11DXsagosTJa2UBHWdcoti4gvzizJDM/r07ZACQbq2MQq/Y/sDQztSQ6oCgzD6TFLs1BOVZN3yEoMS891cHQIPY/AA" rel="noreferrer" title="Wolfram Language (Mathematica) – Try It Online">Try it online!</a></p>

<p>Nonzero values are <a href="https://codegolf.meta.stackexchange.com/a/11884/81203">returned as singleton lists</a>.</p>


blocks|key|909915|text|05AB1E，8+字节数|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|909916|F¯Rćk>Dˆ|code-block|syntax|javascript|909917|在网上试试或输出第一n#qcStackCode#列表中的值.|unstyled|style|CODE|909918|解释：|909919|F+++++++++#+Loop+the+(implicit)+input+amount+of+times:
+¯++++++++#++Push+the+global+array
++R+++++++#++Reverse+it
+++ć++++++#++Extract+the+head;+push+the+remainder+and+the+head+to+the+stack
++++k+++++#++Get+the+0-based+index+of+the+head+in+the+remainder+(-1+if+not+found)
+++++>++++#++Increase+it+by+1+to+make+it+1-indexed+(or+0+if+not+found)
++++++Dˆ++#++Add+a+copy+to+the+global+array
++++++++++#+(after+the+loop,+output+the+top+of+the+stack+implicitly+as+result,
++++++++++#++which+is+why+we+need+the+`D`/duplicate)|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/Adriandmen/05AB1E/wiki/Commands|1|https://github.com/Adriandmen/05AB1E/wiki/Codepage|2|https://tio.run/##yy9OTMpM/f/f7dD6oCPt2XYup9v@/zc1AgA|3|https://tio.run/##yy9OTMpM/f/f7dD6oCPt2Xan22oPrf//39DAAAA^0|0|6|0|9|3|1|0|0|A|E|0|5|2|6|N|3|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@$A|15|B|16|1|17]|$A|18|B|19|1|1A]]|C|$]]|$1|D|3|E|5|F|7|1B|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|1C|8|@$A|1D|B|1E|L|M]]|9|@$A|1F|B|1G|1|1H]|$A|1I|B|1J|1|1K]]|C|$]]|$1|N|3|O|5|6|7|1L|8|@]|9|@]|C|$]]|$1|P|3|Q|5|F|7|1M|8|@]|9|@]|C|$G|H]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]|10|$5|T|U|V|C|$W|11]]|12|$5|T|U|V|C|$W|13]]]]

<h1><a href="https://github.com/Adriandmen/05AB1E/wiki/Commands" rel="nofollow noreferrer">05AB1E</a>, 8 <a href="https://github.com/Adriandmen/05AB1E/wiki/Codepage" rel="nofollow noreferrer">bytes</a></h1>
<pre><code>F¯Rćk&gt;Dˆ
</code></pre>
<p><a href="https://tio.run/##yy9OTMpM/f/f7dD6oCPt2XYup9v@/zc1AgA" rel="nofollow noreferrer">Try it online</a> or <a href="https://tio.run/##yy9OTMpM/f/f7dD6oCPt2Xan22oPrf//39DAAAA" rel="nofollow noreferrer">output the first <span class="math-container">\$n\$</span> values in the list</a>.</p>
<p><strong>Explanation:</strong></p>

<pre class="lang-python prettyprint-override"><code>F         # Loop the (implicit) input amount of times:
 ¯        #  Push the global array
  R       #  Reverse it
   ć      #  Extract the head; push the remainder and the head to the stack
    k     #  Get the 0-based index of the head in the remainder (-1 if not found)
     &gt;    #  Increase it by 1 to make it 1-indexed (or 0 if not found)
      Dˆ  #  Add a copy to the global array
          # (after the loop, output the top of the stack implicitly as result,
          #  which is why we need the `D`/duplicate)
</code></pre>


blocks|key|903585|text|果冻，7字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|903586|Ḷß€ṚiḢ$|code-block|syntax|javascript|903587|在网上试试！|unstyled|903588|0-索引。|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/DennisMitchell/jelly|1|https://tio.run/##y0rNyan8///hjm2H5z9qWvNw56zMhzsWqfw3NAEJtQOF/gMA^0|0|2|0|0|0|0|6|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|L|3|M|5|K|7|15|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

<h1><a href="https://github.com/DennisMitchell/jelly" rel="nofollow noreferrer">Jelly</a>, 7 bytes</h1>

<pre><code>Ḷß€ṚiḢ$
</code></pre>

<p><a href="https://tio.run/##y0rNyan8///hjm2H5z9qWvNw56zMhzsWqfw3NAEJtQOF/gMA" rel="nofollow noreferrer" title="Jelly – Try It Online">Try it online!</a></p>

<p>0-indexed.</p>


blocks|key|909636|text|木炭，23字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|909637|≔⁰θＦ⊖Ｎ«≔⊕⌕⮌υθη⊞υθ≔ηθ»Ｉθ|code-block|syntax|javascript|909638|在网上试试！链接是详细的代码版本。解释：|unstyled|909639|≔⁰θ|909640|将第一个项设置为0。|909641|Ｆ⊖Ｎ«|909642|循环n-1时间。(如果0索引是可以接受的，则可以删除⊖进行1字节保存。)|style|CODE|909643|≔⊕⌕⮌υθη|909644|下一项是前一项反向列表中当前项的递增索引。|909645|⊞υθ|909646|将当前术语添加到以前的术语列表中。|909647|≔ηθ|909648|将当前学期设置为下一学期。|909649|»Ｉθ|909650|在循环结束时打印当前项。|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/somebody1234/Charcoal|1|https://tio.run/##S85ILErOT8z5/9@xuDgzPU/DQEehUNOaKy2/SEHDJTW5KDU3Na8kNUXDM6@gtMSvNDcptUhDU1NToZqLE6rDMw@hyi0zL0UjKLUstag4VaNUE2QWkMgAGsgZUFqcoVEKMR2mNQPCreUKKMrMK9FwTiwu0QDqsP7/39Dyv25ZDgA^0|0|2|0|0|0|0|6|1|0|0|0|0|2|3|Q|1|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@$A|1L|B|1M|1|1N]]|C|$]]|$1|D|3|E|5|F|7|1O|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|1P|8|@]|9|@$A|1Q|B|1R|1|1S]]|C|$]]|$1|L|3|M|5|F|7|1T|8|@]|9|@]|C|$G|H]]|$1|N|3|O|5|K|7|1U|8|@]|9|@]|C|$]]|$1|P|3|Q|5|F|7|1V|8|@]|9|@]|C|$G|H]]|$1|R|3|S|5|K|7|1W|8|@$A|1X|B|1Y|T|U]|$A|1Z|B|20|T|U]]|9|@]|C|$]]|$1|V|3|W|5|F|7|21|8|@]|9|@]|C|$G|H]]|$1|X|3|Y|5|K|7|22|8|@]|9|@]|C|$]]|$1|Z|3|10|5|F|7|23|8|@]|9|@]|C|$G|H]]|$1|11|3|12|5|K|7|24|8|@]|9|@]|C|$]]|$1|13|3|14|5|F|7|25|8|@]|9|@]|C|$G|H]]|$1|15|3|16|5|K|7|26|8|@]|9|@]|C|$]]|$1|17|3|18|5|F|7|27|8|@]|9|@]|C|$G|H]]|$1|19|3|1A|5|K|7|28|8|@]|9|@]|C|$]]]|1B|$1C|$5|1D|1E|1F|C|$1G|1H]]|1I|$5|1D|1E|1F|C|$1G|1J]]]]

<h1><a href="https://github.com/somebody1234/Charcoal" rel="nofollow noreferrer">Charcoal</a>, 23 bytes</h1>

<pre><code>≔⁰θＦ⊖Ｎ«≔⊕⌕⮌υθη⊞υθ≔ηθ»Ｉθ
</code></pre>

<p><a href="https://tio.run/##S85ILErOT8z5/9@xuDgzPU/DQEehUNOaKy2/SEHDJTW5KDU3Na8kNUXDM6@gtMSvNDcptUhDU1NToZqLE6rDMw@hyi0zL0UjKLUstag4VaNUE2QWkMgAGsgZUFqcoVEKMR2mNQPCreUKKMrMK9FwTiwu0QDqsP7/39Dyv25ZDgA" rel="nofollow noreferrer" title="Charcoal – Try It Online">Try it online!</a> Link is to verbose version of code. Explanation:</p>

<pre><code>≔⁰θ
</code></pre>

<p>Set the first term to 0.</p>

<pre><code>Ｆ⊖Ｎ«
</code></pre>

<p>Loop <code>n-1</code> times. (If 0-indexing is acceptable, the <code>⊖</code> can be removed for a 1-byte saving.)</p>

<pre><code>≔⊕⌕⮌υθη
</code></pre>

<p>The next term is the incremented index of the current term in the reversed list of previous terms.</p>

<pre><code>⊞υθ
</code></pre>

<p>Add the current term to the list of previous terms.</p>

<pre><code>≔ηθ
</code></pre>

<p>Set the current term to the next term.</p>

<pre><code>»Ｉθ
</code></pre>

<p>Print the current term at the end of the loop.</p>


blocks|key|910694|text|哈斯克尔，42字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|910695|f+n=last$0:[n-j-1%7Cj<-[0..n-2],f+j==f(n-1)]|code-block|syntax|javascript|910696|在网上试试！|unstyled|910697|其他Haskell回答：66字节和尼米的61个字节。|entityMap|0|LINK|mutability|MUTABLE|url|https://www.haskell.org/|1|https://tio.run/##y0gszk7Nyfn/P00hzzYnsbhExcAqOk83S9ewJstGN9pATy9P1yhWJ00hy9Y2TSNP11Az9n9uYmaegq1CQVFmXomCikKago2KnQJIqaFB7H8A|2|https://codegolf.stackexchange.com/a/186680/3852|3|https://codegolf.stackexchange.com/a/186707/3852^0|0|4|0|0|0|0|6|1|0|C|4|2|H|8|3^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|L|3|M|5|K|7|19|8|@]|9|@$A|1A|B|1B|1|1C]|$A|1D|B|1E|1|1F]]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]|W|$5|P|Q|R|C|$S|X]]|Y|$5|P|Q|R|C|$S|Z]]]]

<h1><a href="https://www.haskell.org/" rel="nofollow noreferrer">Haskell</a>, 42 bytes</h1>

<pre class="lang-hs prettyprint-override"><code>f n=last$0:[n-j-1|j&lt;-[0..n-2],f j==f(n-1)]
</code></pre>
<p><a href="https://tio.run/##y0gszk7Nyfn/P00hzzYnsbhExcAqOk83S9ewJstGN9pATy9P1yhWJ00hy9Y2TSNP11Az9n9uYmaegq1CQVFmXomCikKago2KnQJIqaFB7H8A" rel="nofollow noreferrer" title="Haskell – Try It Online">Try it online!</a></p>
<p>Other Haskell answers: <a href="https://codegolf.stackexchange.com/a/186680/3852">66 bytes by flawr</a> and <a href="https://codegolf.stackexchange.com/a/186707/3852">61 bytes by nimi</a>.</p>


blocks|key|903791|text|C+(gcc)，63字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|903792|f(n){n=g(n,--n);}g(n,i){n=n>0?f(--n)-f(i)?g(n,i)%2B!!g(n,i):1:0;}|code-block|syntax|javascript|903793|在网上试试！|unstyled|903794|0-索引。|entityMap|0|LINK|mutability|MUTABLE|url|https://gcc.gnu.org/|1|https://tio.run/##JcwxCsMwDIXh3adwAgEJW@CMjZrkIl2Kg4KGqiV0Cz67W5Pt53vwMu051ypgeNq8g0UiQy6ttJEtaRVoSAKK6zWErrtiGqfEpb6eaoCnk/cBal@vc2K9jzfWENB9jr8J9MPmafHD9rA@amx3yK7UHw^0|0|7|0|0|0|0|6|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|L|3|M|5|K|7|15|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

<h1><a href="https://gcc.gnu.org/" rel="nofollow noreferrer">C (gcc)</a>, 63 bytes</h1>



<pre class="lang-c prettyprint-override"><code>f(n){n=g(n,--n);}g(n,i){n=n&gt;0?f(--n)-f(i)?g(n,i)+!!g(n,i):1:0;}
</code></pre>

<p><a href="https://tio.run/##JcwxCsMwDIXh3adwAgEJW@CMjZrkIl2Kg4KGqiV0Cz67W5Pt53vwMu051ypgeNq8g0UiQy6ttJEtaRVoSAKK6zWErrtiGqfEpb6eaoCnk/cBal@vc2K9jzfWENB9jr8J9MPmafHD9rA@amx3yK7UHw" rel="nofollow noreferrer" title="C (gcc) – Try It Online">Try it online!</a></p>

<p>0-indexed.</p>


blocks|key|909945|text|Haskell，61字节|type|header-two|depth|inlineStyleRanges|entityRanges|data|909946|(([]#0)1!!)
(l#n)i=n:(((n,i):l)#maybe+0(i-)(lookup+n+l))(i%2B1)|code-block|syntax|javascript|909947|基于0的索引。|unstyled|909948|在网上试试！|offset|length|entityMap|0|LINK|mutability|MUTABLE|url|https://tio.run/##BcHBDoIwDADQu19RMg9tFLIdvJDsS4DDJEwburKAHPx563vvdKyLiOU4GuIwOU@haeiC4pQ4ao@IemfqhVxJ3@cCHrkllG1bzwoKQoR8C2QlsUKEurN@4AolVcgw@K4Lj8l@c5b0Oqyda/0D^0|0|0|0|0|6|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|I|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|I|7|X|8|@]|9|@$L|Y|M|Z|1|10]]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

<h2>Haskell, 61 bytes</h2>

<pre><code>(([]#0)1!!)
(l#n)i=n:(((n,i):l)#maybe 0(i-)(lookup n l))(i+1)
</code></pre>

<p>0-based indexing.</p>

<p><a href="https://tio.run/##BcHBDoIwDADQu19RMg9tFLIdvJDsS4DDJEwburKAHPx563vvdKyLiOU4GuIwOU@haeiC4pQ4ao@IemfqhVxJ3@cCHrkllG1bzwoKQoR8C2QlsUKEurN@4AolVcgw@K4Lj8l@c5b0Oqyda/0D" rel="nofollow noreferrer" title="Haskell – Try It Online">Try it online!</a></p>


blocks|key|904023|text|杰夫特+-h，11字节|type|header-two|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|904024|@ÒZÔÅbX}hTo|code-block|syntax|javascript|904025|试试看|unstyled|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/ETHproductions/japt|1|https://codegolf.meta.stackexchange.com/a/14339/|2|https://petershaggynoble.github.io/Japt-Interpreter/?v=1.4.6&flags=LWg&code=QNJa1MViWH1oVG8&input=NTI^0|4|2|0|3|0|4|2|1|0|0|0|3|2^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]|$9|14|A|15|1|16]]|E|$]]|$1|F|3|G|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|M|7|18|8|@]|D|@$9|19|A|1A|1|1B]]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]|W|$5|P|Q|R|E|$S|X]]]]

<h1><a href="https://github.com/ETHproductions/japt" rel="nofollow noreferrer">Japt</a> <a href="https://codegolf.meta.stackexchange.com/a/14339/"><code>-h</code></a>, 11 bytes</h1>
<pre><code>@ÒZÔÅbX}hTo
</code></pre>
<p><a href="https://petershaggynoble.github.io/Japt-Interpreter/?v=1.4.6&amp;flags=LWg&amp;code=QNJa1MViWH1oVG8&amp;input=NTI" rel="nofollow noreferrer">Try it</a></p>


blocks|key|904175|text|CJam+(15字节)|type|header-two|depth|inlineStyleRanges|entityRanges|data|904176|0a{_(#)\%2B}qi*0=|code-block|syntax|javascript|904177|在线演示在线演示.这是一个完整的程序和0索引.|unstyled|offset|length|904178|解剖|904179|0a++++++e#+Push+the+array+[0]
{+++++++e#+Loop...
++_(#+++e#+++Copy+the+array,+pop+the+first+element,+and+find+its+index+in+the+array
++)\%2B+++e#+++Increment+and+prepend
}qi*++++e#+...+n+times,+where+n+is+read+from+stdin
0=++++++e#+Take+the+first+element+of+the+array|entityMap|0|LINK|mutability|MUTABLE|url|http://cjam.aditsu.net/#code=0a{_(#)\%2B}qi*0=&input=9)|1|http://cjam.aditsu.net/#code=0a{_(#)\%2B}qi*0=&input=9)^0|0|0|0|4|0|4|4|1|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|I|7|10|8|@]|9|@$J|11|K|12|1|13]|$J|14|K|15|1|16]]|A|$]]|$1|L|3|M|5|6|7|17|8|@]|9|@]|A|$]]|$1|N|3|O|5|D|7|18|8|@]|9|@]|A|$E|F]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]]]

<h2>CJam (15 bytes)</h2>

<pre><code>0a{_(#)\+}qi*0=
</code></pre>

<p><a href="http://cjam.aditsu.net/#code=0a%7B_(%23)%5C%2B%7Dqi*0%3D&amp;input=9" rel="nofollow noreferrer">Online demo</a>. This is a full program and 0-indexed.</p>

<h3>Dissection</h3>

<pre><code>0a      e# Push the array [0]
{       e# Loop...
  _(#   e#   Copy the array, pop the first element, and find its index in the array
  )\+   e#   Increment and prepend
}qi*    e# ... n times, where n is read from stdin
0=      e# Take the first element of the array
</code></pre>


blocks|key|910603|text|C#+(可视化C#交互式编译器)，77字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|910604|n=>{int+i,v=0;for(var+m=new+int[n];--n>0;m[v]=n,v=i<1?0:i-n)i=m[v];return+v;}|code-block|syntax|javascript|910605|在网上试试！|unstyled|910606|在这一点上，几乎是Java的一个端口。|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mono-project.com/docs/about-mono/releases/5.0.0/#csc|1|https://tio.run/##HYyxCsMwDAV3f4VGm8TgrFXkbp27hwzFxKAhKjiJM5R@u6t0ePA4jkubTxu3xyFpZNl7XczUhOJHL3BfKWB@F1tfBVaS5QTlk8zovcSA61RnErV4HO7hxl4c0wWxLPtRBCp@GxpzJf5BGlDVEJC7zhmAZ1Fss2XnsP0A^0|0|G|0|0|0|0|6|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|L|3|M|5|K|7|15|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

<h1><a href="http://www.mono-project.com/docs/about-mono/releases/5.0.0/#csc" rel="nofollow noreferrer">C# (Visual C# Interactive Compiler)</a>, 77 bytes</h1>



<pre class="lang-cs prettyprint-override"><code>n=&gt;{int i,v=0;for(var m=new int[n];--n&gt;0;m[v]=n,v=i&lt;1?0:i-n)i=m[v];return v;}
</code></pre>

<p><a href="https://tio.run/##HYyxCsMwDAV3f4VGm8TgrFXkbp27hwzFxKAhKjiJM5R@u6t0ePA4jkubTxu3xyFpZNl7XczUhOJHL3BfKWB@F1tfBVaS5QTlk8zovcSA61RnErV4HO7hxl4c0wWxLPtRBCp@GxpzJf5BGlDVEJC7zhmAZ1Fss2XnsP0A" rel="nofollow noreferrer" title="C# (Visual C# Interactive Compiler) – Try It Online">Try it online!</a></p>

<p>Pretty much a port of the Java answer at this point.</p>


blocks|key|910761|text|维沙尔，8字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|910762|W?(p:ḣḟ›|code-block|syntax|javascript|910763|在网上试试！+1-索引。|unstyled|910764|解释：|910765|从a(n)+<+n开始，我们可以将n推到列表的开头。还向后构建序列。|style|CODE|910766|W?(p:ḣḟ›+#+whole+program

W++++++++#+[]
+?+++++++#++++++++++++input
++(++++++#+repeat+for+++++++times:
+++p+++++#++prepend+to+list+(uses+implicit+input+the+first+time)
++++:++++#++duplicate
+++++ḣ+++#++split+head+from+the+rest
++++++ḟ++#++find+its+index+on+the+list+(-1+if+none)
+++++++›+#++increment
+++++++++#+as+we+didn't+prepend+the+last+item,+output+it+|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/Vyxal/Vyxal|1|https://vyxal.pythonanywhere.com/#WyJBIiwiIiwiVz8ocDrhuKPhuJ/igLoiLCIiLCIxXG44XG4xOVxuMjdcbjUyXG42NCJd|2|INLINETEX|IMMUTABLE|teX|a(n)+<+n|3|n^0|0|3|0|0|0|0|6|1|0|0|1|8|H|1|1|8|2|H|1|3|0^^$0|@$1|2|3|4|5|6|7|19|8|@]|9|@$A|1A|B|1B|1|1C]]|C|$]]|$1|D|3|E|5|F|7|1D|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|1E|8|@]|9|@$A|1F|B|1G|1|1H]]|C|$]]|$1|L|3|M|5|6|7|1I|8|@]|9|@]|C|$]]|$1|N|3|O|5|K|7|1J|8|@$A|1K|B|1L|P|Q]|$A|1M|B|1N|P|Q]]|9|@$A|1O|B|1P|1|1Q]|$A|1R|B|1S|1|1T]]|C|$]]|$1|R|3|S|5|F|7|1U|8|@]|9|@]|C|$G|H]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|11]]|12|$5|13|W|14|C|$15|16]]|17|$5|13|W|14|C|$15|18]]]]

<h1><a href="https://github.com/Vyxal/Vyxal" rel="nofollow noreferrer">Vyxal</a>, 8 bytes</h1>
<pre><code>W?(p:ḣḟ›
</code></pre>
<p><a href="https://vyxal.pythonanywhere.com/#WyJBIiwiIiwiVz8ocDrhuKPhuJ/igLoiLCIiLCIxXG44XG4xOVxuMjdcbjUyXG42NCJd" rel="nofollow noreferrer">Try it Online!</a> 1-indexed.</p>
<p><strong>Explanation:</strong></p>
<p>Since <span class="math-container">\$a(n) &lt; n\$</span>, we can push <span class="math-container">\$n\$</span> to the beginning of the list. Also builds the sequence backwards.</p>
<pre><code>W?(p:ḣḟ› # whole program

W        # []
 ?       #            input
  (      # repeat for       times:
   p     #  prepend to list (uses implicit input the first time)
    :    #  duplicate
     ḣ   #  split head from the rest
      ḟ  #  find its index on the list (-1 if none)
       › #  increment
         # as we didn't prepend the last item, output it 
</code></pre>


blocks|key|903537|text|Python+3，112个字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|903538|a=[0]
for+_+in+a*int(input()):k=a[-1];a%2B=k+in+a[:-1]and[a[::-1].index(k)%2B~a[-2::-1].index(k)]or[0]
print(-a[-2])|code-block|syntax|javascript|903539|在网上试试！|unstyled|903540|-感谢我的3字节|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/|1|https://tio.run/##K6gsycjPM/7/P9E22iCWKy2/SCFeITNPIVErM69EIzOvoLREQ1PTKts2MVrXMNY6Uds2GywdbQXkJualRANZIKZeZl5KaoVGtqZ2HVClEapYbH4RyPCCIpCZuiD5WM3//43MAQ^0|0|8|0|0|0|0|6|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|L|3|M|5|K|7|15|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

<h1><a href="https://docs.python.org/3/" rel="nofollow noreferrer">Python 3</a>, 112 bytes</h1>



<pre class="lang-python prettyprint-override"><code>a=[0]
for _ in a*int(input()):k=a[-1];a+=k in a[:-1]and[a[::-1].index(k)+~a[-2::-1].index(k)]or[0]
print(-a[-2])
</code></pre>

<p><a href="https://tio.run/##K6gsycjPM/7/P9E22iCWKy2/SCFeITNPIVErM69EIzOvoLREQ1PTKts2MVrXMNY6Uds2GywdbQXkJualRANZIKZeZl5KaoVGtqZ2HVClEapYbH4RyPCCIpCZuiD5WM3//43MAQ" rel="nofollow noreferrer" title="Python 3 – Try It Online">Try it online!</a></p>

<p>-3 bytes thanks to mypetlion</p>


blocks|key|904338|text|皮斯，18字节|type|header-two|depth|inlineStyleRanges|entityRanges|offset|length|data|904339|VQ=Y%2B?YhxtYhY0Y;hY|code-block|syntax|javascript|904340|在网上试试！|unstyled|904341|反向构建序列并打印第一个元素(序列的最后一个项)。|904342|VQ+++++++++++++++++#+for+N+in+range(Q)+(Q=input)
++=Y%2B+++++++++Y++++#+Y.prepend(
++++++++xtY++++++++#+++Y[1:].index(++++)
+++++++++++hY++++++#+++++++++++++++Y[0]
+++++++h+++++++++++#+++++++++++++++++++++%2B1
+++++?Y++++++0+++++#++++++++++++++++++++++++if+Y+else+0)
+++++++++++++++;hY+#+end+for+loop+and+print+Y[0]|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/isaacg1/pyth|1|https://tio.run/##K6gsyfj/PyzQNlLbPjKjoiQyI9Ig0joj8v9/UyMA^0|0|2|0|0|0|0|6|1|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|K|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|L|3|M|5|K|7|17|8|@]|9|@]|C|$]]|$1|N|3|O|5|F|7|18|8|@]|9|@]|C|$G|H]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]]]

<h1><a href="https://github.com/isaacg1/pyth" rel="nofollow noreferrer">Pyth</a>, 18 bytes</h1>

<pre><code>VQ=Y+?YhxtYhY0Y;hY
</code></pre>

<p><a href="https://tio.run/##K6gsyfj/PyzQNlLbPjKjoiQyI9Ig0joj8v9/UyMA" rel="nofollow noreferrer" title="Pyth – Try It Online">Try it online!</a></p>

<p>Builds up the sequence in reverse and prints the first element (last term of the sequence).</p>

<pre><code>VQ                 # for N in range(Q) (Q=input)
  =Y+         Y    # Y.prepend(
        xtY        #   Y[1:].index(    )
           hY      #               Y[0]
       h           #                     +1
     ?Y      0     #                        if Y else 0)
               ;hY # end for loop and print Y[0]
</code></pre>


blocks|key|904551|text|Arn+-f，13个字节|type|header-two|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|904552|f→S›J⁻åƒƒN5═%25|code-block|syntax|javascript|904553|试试看！+0-索引|unstyled|904554|解释了|904555|解压缩：&.{%2B%2B.{:i:{)%7C}[|904556|&.++++++++++++Mutate+S+N+times
++{+++++++++++++With+block,+key+of+`_`
++++++%2B%2B++++++++Increment
++++++++++++_+++Implicit
++++++++++.{++++Behead
++++++++:i++++++Index+of
++++++++++++_+++Implicit
++++++++++:{++++Head
++++++)+++++Don't+ask
++++%7C+++++++++++Concatenated+with
++++++_+++++++++Implicit
++}+++++++++++++End+block
++[+++++++++++Where+S+is+an+array
++]+++++++++++++Ending+implicit
++_+++++++++++And+N+is+STDIN;+implicit
++++++++++++Then+take+the+head|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/ZippyMagician/Arn|1|https://github.com/ZippyMagician/Arn/wiki/Carn|2|https://zippymagician.github.io/Arn?code=Ji57KysuezppOnspfH1b&input=MQo4CjE5CjI3CjUyCjY0&flags=Zg==^0|4|2|0|3|0|7|5|1|0|0|0|4|2|0|0|4|F|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]|$9|1A|A|1B|1|1C]]|E|$]]|$1|F|3|G|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|M|7|1E|8|@]|D|@$9|1F|A|1G|1|1H]]|E|$]]|$1|N|3|O|5|6|7|1I|8|@]|D|@]|E|$]]|$1|P|3|Q|5|M|7|1J|8|@$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|R|3|S|5|H|7|1M|8|@]|D|@]|E|$I|J]]]|T|$U|$5|V|W|X|E|$Y|Z]]|10|$5|V|W|X|E|$Y|11]]|12|$5|V|W|X|E|$Y|13]]]]

<h1><a href="https://github.com/ZippyMagician/Arn" rel="nofollow noreferrer">Arn</a> <code>-f</code>, <a href="https://github.com/ZippyMagician/Arn/wiki/Carn" rel="nofollow noreferrer">13 bytes</a></h1>
<pre><code>f→S›J⁻åƒƒN5═%
</code></pre>
<p><a href="https://zippymagician.github.io/Arn?code=Ji57KysuezppOnspfH1b&amp;input=MQo4CjE5CjI3CjUyCjY0&amp;flags=Zg==" rel="nofollow noreferrer">Try it!</a>
0-indexed</p>
<h1>Explained</h1>
<p>Unpacked: <code>&amp;.{++.{:i:{)|}[</code></p>
<pre><code>&amp;.            Mutate S N times
  {             With block, key of `_`
      ++        Increment
            _   Implicit
          .{    Behead
        :i      Index of
            _   Implicit
          :{    Head
      )     Don't ask
    |           Concatenated with
      _         Implicit
  }             End block
  [           Where S is an array
  ]             Ending implicit
  _           And N is STDIN; implicit
            Then take the head
</code></pre>


blocks|key|910531|text|Clojure，69字节|type|header-two|depth|inlineStyleRanges|entityRanges|data|910532|#((fn+f[i+c+t](if(=+i+1)t(f(dec+i)(assoc+c+t+i)(-(or(c+t)i)i))))%25{}0)|code-block|syntax|javascript|910533|可悲的是，一种更有效的方法似乎要长一些。|unstyled|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|I|7|M|8|@]|9|@]|A|$]]]|J|$]]

<h2>Clojure, 69 bytes</h2>

<pre><code>#((fn f[i c t](if(= i 1)t(f(dec i)(assoc c t i)(-(or(c t)i)i))))%{}0)
</code></pre>

<p>Sadly a more functional approach seems to be longer.</p>


<p>Output the Nth term of the Van Eck Sequence.</p>

<p>Van Eck Sequence is defined as:</p>

<ul>
<li>Starts with 0. </li>
<li>If the last term is the first occurrence of that term the next term is 0. </li>
<li>If the last term has occurred previously the next term is how many steps back was the most recent occurrence.</li>
</ul>

<p><a href="https://oeis.org/A181391" rel="noreferrer">https://oeis.org/A181391</a></p>

<p><a href="https://www.youtube.com/watch?v=etMJxB-igrc" rel="noreferrer">https://www.youtube.com/watch?v=etMJxB-igrc</a></p>

<p><a href="https://www.youtube.com/watch?v=8VrnqRU7BVU" rel="noreferrer">https://www.youtube.com/watch?v=8VrnqRU7BVU</a></p>

<p>Sequence: 
0,0,1,0,2,0,2,2,1,6,0,5,0,2,...</p>

<p>Tests:</p>

<p>Input | Output</p>

<ul>
<li>1  | 0 </li>
<li>8  | 2 </li>
<li>19 | 5 </li>
<li>27 | 9 </li>
<li>52 | 42</li>
<li>64 | 0</li>
</ul>

<p><strong>EDIT</strong></p>

<p>1 indexed is preferred, 0 indexed is acceptable; that might change some of the already submitted solutions.</p>

<p>Just the Nth term please.</p>

<p>Same (except for the seeing it already posted part), it seems code golfers and numberphile watchers have a decent overlap.</p>


Nth term of Van Eck Sequence

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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功能1上新10个字符

功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符。

功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符。

功能5描述100个字符功能5描述100个字符功能5描述100个字符功能5描述100个字符功能5描述100个字符功能5描述100个字符

功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符

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输出Van Eck序列的第N项。Van Eck序列被定义为：从0开始。如果最后一项是该项的第一次出现，则下一项为0。如果最后一项发生在前面，下一项是最近发生的后退多少步。https://oeis.org/A181391https://www.youtube.com/watch?v=etMJxB-igrchttps://www.youtube.com/watch?v=8VrnqRU7BVU顺序:0，

问Van Eck序列的第n项
EN

编辑

回答 17

Code Golf用户

R，62字节

Code Golf用户

Python，51字节

Code Golf用户

Wolfram语言(数学)，48字节

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问Van Eck序列的第n项EN

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回答 17

Code Golf用户

R，62字节

Code Golf用户

Python，51字节

Code Golf用户

Wolfram语言(数学)，48字节

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问Van Eck序列的第n项
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