235 lines
8.7 KiB
Plaintext
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235 lines
8.7 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<meta charset="utf-8">
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<title>Go by Example: Recursion</title>
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<div class="example" id="recursion">
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<h2><a href="./">Go by Example</a>: Recursion</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Go supports
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<a href="https://en.wikipedia.org/wiki/Recursion_(computer_science)"><em>recursive functions</em></a>.
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Here’s a classic example.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="https://go.dev/play/p/MBTKk9VpAiK"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>This <code>fact</code> function calls itself until it reaches the
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base case of <code>fact(0)</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="kd">func</span> <span class="nf">fact</span><span class="p">(</span><span class="nx">n</span> <span class="kt">int</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">n</span> <span class="o">==</span> <span class="mi">0</span> <span class="p">{</span>
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<span class="k">return</span> <span class="mi">1</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="nx">n</span> <span class="o">*</span> <span class="nf">fact</span><span class="p">(</span><span class="nx">n</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">fact</span><span class="p">(</span><span class="mi">7</span><span class="p">))</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Closures can also be recursive, but this requires the
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closure to be declared with a typed <code>var</code> explicitly
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before it’s defined.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="kd">var</span> <span class="nx">fib</span> <span class="kd">func</span><span class="p">(</span><span class="nx">n</span> <span class="kt">int</span><span class="p">)</span> <span class="kt">int</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"> <span class="nx">fib</span> <span class="p">=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">n</span> <span class="kt">int</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">n</span> <span class="p"><</span> <span class="mi">2</span> <span class="p">{</span>
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<span class="k">return</span> <span class="nx">n</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Since <code>fib</code> was previously declared in <code>main</code>, Go
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knows which function to call with <code>fib</code> here.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="k">return</span> <span class="nf">fib</span><span class="p">(</span><span class="nx">n</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="nf">fib</span><span class="p">(</span><span class="nx">n</span><span class="o">-</span><span class="mi">2</span><span class="p">)</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code">
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<pre class="chroma"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">fib</span><span class="p">(</span><span class="mi">7</span><span class="p">))</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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</td>
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<td class="code">
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<pre class="chroma"><span class="gp">$</span> go run recursion.go
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<span class="go">5040
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</span><span class="go">13</span></pre>
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="pointers">Pointers</a>.
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> | <button id="theme-button">Toggle theme</button>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func fact(n int) int {\u000A if n \u003D\u003D 0 {\u000A return 1\u000A }\u000A return n * fact(n-1)\u000A}\u000A');codeLines.push('func main() {\u000A fmt.Println(fact(7))\u000A');codeLines.push(' var fib func(n int) int\u000A');codeLines.push(' fib \u003D func(n int) int {\u000A if n \u003C 2 {\u000A return n\u000A }\u000A');codeLines.push(' return fib(n-1) + fib(n-2)\u000A }\u000A');codeLines.push(' fmt.Println(fib(7))\u000A}\u000A');codeLines.push('');
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