137 lines
22 KiB
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137 lines
22 KiB
HTML
<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Wrap abstract fragments into lines with a first-fit algorithm."><meta name="keywords" content="rust, rustlang, rust-lang, wrap_first_fit"><title>wrap_first_fit in textwrap::wrap_algorithms - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script src="../../crates.js"></script><script defer src="../../main.js"></script>
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</a><div class="sidebar-elems"><h2 class="location">Other items in<br><a href="../index.html">textwrap</a>::<wbr><a href="index.html">wrap_algorithms</a></h2><div id="sidebar-vars" data-name="wrap_first_fit" data-ty="fn" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../../textwrap/index.html"><img class="rust-logo" src="../../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" id="help-button" title="help">?</button><a id="settings-menu" href="../../settings.html" title="settings"><img width="18" height="18" alt="Change settings" src="../../wheel.svg"></a></div></form></nav></div><section id="main-content" class="content"><h1 class="fqn"><span class="in-band">Function <a href="../index.html">textwrap</a>::<wbr><a href="index.html">wrap_algorithms</a>::<wbr><a class="fn" href="#">wrap_first_fit</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../../src/textwrap/wrap_algorithms.rs.html#315-339" title="goto source code">[src]</a></span></h1><div class="docblock item-decl"><pre class="rust fn"><code>pub fn wrap_first_fit<'a, 'b, T: <a class="trait" href="../core/trait.Fragment.html" title="trait textwrap::core::Fragment">Fragment</a>>(<br> fragments: <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.slice.html">&'a [T]</a>, <br> line_widths: <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.slice.html">&'b [</a><a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.f64.html">f64</a><a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.slice.html">]</a><br>) -> <a class="struct" href="https://doc.rust-lang.org/1.59.0/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a><<a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.slice.html">&'a [T]</a>></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Wrap abstract fragments into lines with a first-fit algorithm.</p>
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<p>The <code>line_widths</code> slice gives the target line width for each line
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(the last slice element is repeated as necessary). This can be
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used to implement hanging indentation.</p>
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<p>The fragments must already have been split into the desired
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widths, this function will not (and cannot) attempt to split them
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further when arranging them into lines.</p>
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<h2 id="first-fit-algorithm" class="section-header"><a href="#first-fit-algorithm">First-Fit Algorithm</a></h2>
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<p>This implements a simple “greedy” algorithm: accumulate fragments
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one by one and when a fragment no longer fits, start a new line.
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There is no look-ahead, we simply take first fit of the fragments
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we find.</p>
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<p>While fast and predictable, this algorithm can produce poor line
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breaks when a long fragment is moved to a new line, leaving behind
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a large gap:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">textwrap::core::Word</span>;
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<span class="kw">use</span> <span class="ident">textwrap::wrap_algorithms::wrap_first_fit</span>;
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<span class="kw">use</span> <span class="ident">textwrap::WordSeparator</span>;
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<span class="comment">// Helper to convert wrapped lines to a Vec<String>.</span>
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<span class="kw">fn</span> <span class="ident">lines_to_strings</span>(<span class="ident">lines</span>: <span class="ident">Vec</span><span class="op"><</span><span class="kw-2">&</span>[<span class="ident">Word</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>]<span class="op">></span>) -> <span class="ident">Vec</span><span class="op"><</span><span class="ident">String</span><span class="op">></span> {
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<span class="ident">lines</span>.<span class="ident">iter</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">line</span><span class="op">|</span> {
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<span class="ident">line</span>.<span class="ident">iter</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">word</span><span class="op">|</span> <span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">word</span>).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">></span><span class="op">></span>().<span class="ident">join</span>(<span class="string">" "</span>)
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}).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">></span><span class="op">></span>()
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}
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<span class="kw">let</span> <span class="ident">text</span> <span class="op">=</span> <span class="string">"These few words will unfortunately not wrap nicely."</span>;
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<span class="kw">let</span> <span class="ident">words</span> <span class="op">=</span> <span class="ident">WordSeparator::AsciiSpace</span>.<span class="ident">find_words</span>(<span class="ident">text</span>).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">></span><span class="op">></span>();
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<span class="macro">assert_eq!</span>(<span class="ident">lines_to_strings</span>(<span class="ident">wrap_first_fit</span>(<span class="kw-2">&</span><span class="ident">words</span>, <span class="kw-2">&</span>[<span class="number">15.0</span>])),
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<span class="macro">vec!</span>[<span class="string">"These few words"</span>,
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<span class="string">"will"</span>, <span class="comment">// <-- short line</span>
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<span class="string">"unfortunately"</span>,
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<span class="string">"not wrap"</span>,
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<span class="string">"nicely."</span>]);
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<span class="comment">// We can avoid the short line if we look ahead:</span>
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<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"smawk"</span>)]</span>
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<span class="kw">use</span> <span class="ident">textwrap::wrap_algorithms</span>::{<span class="ident">wrap_optimal_fit</span>, <span class="ident">Penalties</span>};
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<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"smawk"</span>)]</span>
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<span class="macro">assert_eq!</span>(<span class="ident">lines_to_strings</span>(<span class="ident">wrap_optimal_fit</span>(<span class="kw-2">&</span><span class="ident">words</span>, <span class="kw-2">&</span>[<span class="number">15.0</span>], <span class="kw-2">&</span><span class="ident">Penalties::new</span>()).<span class="ident">unwrap</span>()),
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<span class="macro">vec!</span>[<span class="string">"These few"</span>,
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<span class="string">"words will"</span>,
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<span class="string">"unfortunately"</span>,
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<span class="string">"not wrap"</span>,
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<span class="string">"nicely."</span>]);</code></pre></div>
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<p>The [<code>wrap_optimal_fit</code>] function was used above to get better
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line breaks. It uses an advanced algorithm which tries to avoid
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short lines. This function is about 4 times faster than
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[<code>wrap_optimal_fit</code>].</p>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<p>Imagine you’re building a house site and you have a number of
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tasks you need to execute. Things like pour foundation, complete
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framing, install plumbing, electric cabling, install insulation.</p>
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<p>The construction workers can only work during daytime, so they
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need to pack up everything at night. Because they need to secure
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their tools and move machines back to the garage, this process
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takes much more time than the time it would take them to simply
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switch to another task.</p>
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<p>You would like to make a list of tasks to execute every day based
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on your estimates. You can model this with a program like this:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">textwrap::core</span>::{<span class="ident">Fragment</span>, <span class="ident">Word</span>};
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<span class="kw">use</span> <span class="ident">textwrap::wrap_algorithms::wrap_first_fit</span>;
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
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<span class="kw">struct</span> <span class="ident">Task</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
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<span class="ident">name</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>,
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<span class="ident">hours</span>: <span class="ident">f64</span>, <span class="comment">// Time needed to complete task.</span>
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<span class="ident">sweep</span>: <span class="ident">f64</span>, <span class="comment">// Time needed for a quick sweep after task during the day.</span>
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<span class="ident">cleanup</span>: <span class="ident">f64</span>, <span class="comment">// Time needed for full cleanup if day ends with this task.</span>
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}
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<span class="kw">impl</span> <span class="ident">Fragment</span> <span class="kw">for</span> <span class="ident">Task</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span> {
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<span class="kw">fn</span> <span class="ident">width</span>(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="ident">f64</span> { <span class="self">self</span>.<span class="ident">hours</span> }
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<span class="kw">fn</span> <span class="ident">whitespace_width</span>(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="ident">f64</span> { <span class="self">self</span>.<span class="ident">sweep</span> }
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<span class="kw">fn</span> <span class="ident">penalty_width</span>(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="ident">f64</span> { <span class="self">self</span>.<span class="ident">cleanup</span> }
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}
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<span class="comment">// The morning tasks</span>
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<span class="kw">let</span> <span class="ident">tasks</span> <span class="op">=</span> <span class="macro">vec!</span>[
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Foundation"</span>, <span class="ident">hours</span>: <span class="number">4.0</span>, <span class="ident">sweep</span>: <span class="number">2.0</span>, <span class="ident">cleanup</span>: <span class="number">3.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Framing"</span>, <span class="ident">hours</span>: <span class="number">3.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Plumbing"</span>, <span class="ident">hours</span>: <span class="number">2.0</span>, <span class="ident">sweep</span>: <span class="number">2.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Electrical"</span>, <span class="ident">hours</span>: <span class="number">2.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Insulation"</span>, <span class="ident">hours</span>: <span class="number">2.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Drywall"</span>, <span class="ident">hours</span>: <span class="number">3.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Floors"</span>, <span class="ident">hours</span>: <span class="number">3.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Countertops"</span>, <span class="ident">hours</span>: <span class="number">1.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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<span class="ident">Task</span> { <span class="ident">name</span>: <span class="string">"Bathrooms"</span>, <span class="ident">hours</span>: <span class="number">2.0</span>, <span class="ident">sweep</span>: <span class="number">1.0</span>, <span class="ident">cleanup</span>: <span class="number">2.0</span> },
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];
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<span class="comment">// Fill tasks into days, taking `day_length` into account. The</span>
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<span class="comment">// output shows the hours worked per day along with the names of</span>
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<span class="comment">// the tasks for that day.</span>
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<span class="kw">fn</span> <span class="ident">assign_days</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="ident">tasks</span>: <span class="kw-2">&</span>[<span class="ident">Task</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>], <span class="ident">day_length</span>: <span class="ident">f64</span>) -> <span class="ident">Vec</span><span class="op"><</span>(<span class="ident">f64</span>, <span class="ident">Vec</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span><span class="op">></span>)<span class="op">></span> {
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">days</span> <span class="op">=</span> <span class="ident">Vec::new</span>();
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<span class="comment">// Assign tasks to days. The assignment is a vector of slices,</span>
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<span class="comment">// with a slice per day.</span>
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<span class="kw">let</span> <span class="ident">assigned_days</span>: <span class="ident">Vec</span><span class="op"><</span><span class="kw-2">&</span>[<span class="ident">Task</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>]<span class="op">></span> <span class="op">=</span> <span class="ident">wrap_first_fit</span>(<span class="kw-2">&</span><span class="ident">tasks</span>, <span class="kw-2">&</span>[<span class="ident">day_length</span>]);
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<span class="kw">for</span> <span class="ident">day</span> <span class="kw">in</span> <span class="ident">assigned_days</span>.<span class="ident">iter</span>() {
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<span class="kw">let</span> <span class="ident">last</span> <span class="op">=</span> <span class="ident">day</span>.<span class="ident">last</span>().<span class="ident">unwrap</span>();
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<span class="kw">let</span> <span class="ident">work_hours</span>: <span class="ident">f64</span> <span class="op">=</span> <span class="ident">day</span>.<span class="ident">iter</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">t</span><span class="op">|</span> <span class="ident">t</span>.<span class="ident">hours</span> <span class="op">+</span> <span class="ident">t</span>.<span class="ident">sweep</span>).<span class="ident">sum</span>();
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<span class="kw">let</span> <span class="ident">names</span> <span class="op">=</span> <span class="ident">day</span>.<span class="ident">iter</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">t</span><span class="op">|</span> <span class="ident">t</span>.<span class="ident">name</span>).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">></span><span class="op">></span>();
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<span class="ident">days</span>.<span class="ident">push</span>((<span class="ident">work_hours</span> <span class="op">-</span> <span class="ident">last</span>.<span class="ident">sweep</span> <span class="op">+</span> <span class="ident">last</span>.<span class="ident">cleanup</span>, <span class="ident">names</span>));
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}
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<span class="ident">days</span>
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}
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<span class="comment">// With a single crew working 8 hours a day:</span>
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<span class="macro">assert_eq!</span>(
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<span class="ident">assign_days</span>(<span class="kw-2">&</span><span class="ident">tasks</span>, <span class="number">8.0</span>),
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[
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(<span class="number">7.0</span>, <span class="macro">vec!</span>[<span class="string">"Foundation"</span>]),
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(<span class="number">8.0</span>, <span class="macro">vec!</span>[<span class="string">"Framing"</span>, <span class="string">"Plumbing"</span>]),
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(<span class="number">7.0</span>, <span class="macro">vec!</span>[<span class="string">"Electrical"</span>, <span class="string">"Insulation"</span>]),
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(<span class="number">5.0</span>, <span class="macro">vec!</span>[<span class="string">"Drywall"</span>]),
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(<span class="number">7.0</span>, <span class="macro">vec!</span>[<span class="string">"Floors"</span>, <span class="string">"Countertops"</span>]),
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(<span class="number">4.0</span>, <span class="macro">vec!</span>[<span class="string">"Bathrooms"</span>]),
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]
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);
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<span class="comment">// With two crews working in shifts, 16 hours a day:</span>
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<span class="macro">assert_eq!</span>(
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<span class="ident">assign_days</span>(<span class="kw-2">&</span><span class="ident">tasks</span>, <span class="number">16.0</span>),
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[
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(<span class="number">14.0</span>, <span class="macro">vec!</span>[<span class="string">"Foundation"</span>, <span class="string">"Framing"</span>, <span class="string">"Plumbing"</span>]),
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(<span class="number">15.0</span>, <span class="macro">vec!</span>[<span class="string">"Electrical"</span>, <span class="string">"Insulation"</span>, <span class="string">"Drywall"</span>, <span class="string">"Floors"</span>]),
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(<span class="number">6.0</span>, <span class="macro">vec!</span>[<span class="string">"Countertops"</span>, <span class="string">"Bathrooms"</span>]),
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]
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);</code></pre></div>
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<p>Apologies to anyone who actually knows how to build a house and
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knows how long each step takes :-)</p>
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</div></details></section><section id="search" class="content hidden"></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="textwrap" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.59.0 (9d1b2106e 2022-02-23)" ></div>
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