{"data":{"site":{"siteMetadata":{"title":"HOME | blackpudding","subtitle":"고생했어. 오늘도.","copyright":"© All rights reserved.","author":{"name":"William JO","github":"blackpudding96"},"disqusShortname":"blackpudding","url":"https://blackpudding.netlify.com"}},"markdownRemark":{"id":"b7b2c91f-0322-5d9e-9b78-265dd3837acc","html":"<h1>2355번 : 시그마</h1>\n<p>👉 <a href=\"https://www.acmicpc.net/problem/2355\">문제 바로가기</a></p>\n<h2>배경 지식</h2>\n<ul>\n<li><code class=\"language-text\">등차수열</code> : 첫째항부터 차례로 일정한 수를 더하여 만든 수열. 이때 더하는 일정한 수를 공차라고 한다.</li>\n<li><code class=\"language-text\">등차수열의 합</code> : 첫째항이 a, 공차가 d, 제 n항이 l인 등차수열의 첫째항부터 제 n항까지의 합을 Sn이라 하면 아래와 같다.\n\n  <a\n    class=\"gatsby-resp-image-link\"\n    href=\"/static/sum_of_arithmetic_progression-b9c98eb0d99cc8bb0eee580c51ad49ab-75384.png\"\n    style=\"display: block\"\n    target=\"_blank\"\n    rel=\"noopener\"\n  >\n  \n  <span\n    class=\"gatsby-resp-image-wrapper\"\n    style=\"position: relative; display: block;  max-width: 239px; margin-left: auto; margin-right: auto;\"\n  >\n    <span\n      class=\"gatsby-resp-image-background-image\"\n      style=\"padding-bottom: 43.51464435146444%; position: relative; bottom: 0; left: 0; background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAJCAIAAAC9o5sfAAAACXBIWXMAAAsSAAALEgHS3X78AAABKElEQVQoz21RyW6DMBD1//9Wc6iqXqqELQtLA8TGJtgY25hg0mlQk6jkHUZvRm92dL1hmqaZOOdqRklFO6W0NkqKNPu+jOP1FZBzk5JSaTP7wzD46y/fD5MkbYVglO72e2vtc4NHMj3zbbBZe6HRuihKawcuRM1YVVWEEM45ZWwYLv/S5kLocoOUcnSPycGeyuIQx3fdc9s7R8t6AGt7wbk2Zg7O5WbeWwuuVgosuuf97WyjKAq8zefH+7HEbdtyLnaRnx0LGL43Kt5vgzBava063SM4apYcihNx49g0DayAMc4AaYorKn6TeUVwfW66Dj6g8KnM8zyOU3gGYvWZlPl2dzDGgA6uDfsLIUAqW9ne4PseyIBAHMpJ2QEDPVo+YIkoDJSxy/gPBQoEF3VfjUcAAAAASUVORK5CYII='); background-size: cover; display: block;\"\n    >\n      <img\n        class=\"gatsby-resp-image-image\"\n        style=\"width: 100%; height: 100%; margin: 0; vertical-align: middle; position: absolute; top: 0; left: 0; box-shadow: inset 0px 0px 0px 400px white;\"\n        alt=\"등차수열의 합\"\n        title=\"\"\n        src=\"/static/sum_of_arithmetic_progression-b9c98eb0d99cc8bb0eee580c51ad49ab-75384.png\"\n        srcset=\"/static/sum_of_arithmetic_progression-b9c98eb0d99cc8bb0eee580c51ad49ab-75384.png 239w\"\n        sizes=\"(max-width: 239px) 100vw, 239px\"\n      />\n    </span>\n  </span>\n  \n  </a>\n    </li>\n</ul>\n<h2>푼 방법</h2>\n<p>등차수열의 합의 공식을 이용해서 풀었다.</p>\n<p>조심해야 할 것은, 문제에서 a와 b의 대소 관계에 대한 내용은 언급하지 않았다는 것이다!</p>\n<h2>내 정답 코드 (C++)</h2>\n<div class=\"gatsby-highlight\" data-language=\"c\"><pre class=\"language-c\"><code class=\"language-c\"><span class=\"token macro property\">#<span class=\"token directive keyword\">include</span> <span class=\"token string\">&lt;iostream></span></span>\n<span class=\"token macro property\">#<span class=\"token directive keyword\">define</span> SWAP(a, b) {a^=b^=a^=b;}</span>\n\n<span class=\"token keyword\">int</span> <span class=\"token function\">main</span><span class=\"token punctuation\">(</span><span class=\"token punctuation\">)</span> <span class=\"token punctuation\">{</span>\n\tstd<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span>ios<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span><span class=\"token function\">sync_with_stdio</span><span class=\"token punctuation\">(</span>false<span class=\"token punctuation\">)</span><span class=\"token punctuation\">;</span>\n\tstd<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span>cin<span class=\"token punctuation\">.</span><span class=\"token function\">tie</span><span class=\"token punctuation\">(</span><span class=\"token constant\">NULL</span><span class=\"token punctuation\">)</span><span class=\"token punctuation\">;</span> \n\tstd<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span>cout<span class=\"token punctuation\">.</span><span class=\"token function\">tie</span><span class=\"token punctuation\">(</span><span class=\"token constant\">NULL</span><span class=\"token punctuation\">)</span><span class=\"token punctuation\">;</span>\n\t\n\t<span class=\"token keyword\">long</span> <span class=\"token keyword\">long</span> <span class=\"token keyword\">int</span> a<span class=\"token punctuation\">,</span> b<span class=\"token punctuation\">;</span>\n\t\n\tstd<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span>cin <span class=\"token operator\">>></span> a <span class=\"token operator\">>></span> b<span class=\"token punctuation\">;</span>\n\t\n\t<span class=\"token keyword\">if</span> <span class=\"token punctuation\">(</span>a <span class=\"token operator\">></span> b<span class=\"token punctuation\">)</span> <span class=\"token function\">SWAP</span><span class=\"token punctuation\">(</span>a<span class=\"token punctuation\">,</span> b<span class=\"token punctuation\">)</span><span class=\"token punctuation\">;</span>\n\t\n\tstd<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span>cout <span class=\"token operator\">&lt;&lt;</span> <span class=\"token punctuation\">(</span><span class=\"token punctuation\">(</span>b<span class=\"token operator\">-</span>a<span class=\"token operator\">+</span><span class=\"token number\">1</span><span class=\"token punctuation\">)</span> <span class=\"token operator\">*</span> <span class=\"token punctuation\">(</span>a<span class=\"token operator\">+</span>b<span class=\"token punctuation\">)</span><span class=\"token punctuation\">)</span> <span class=\"token operator\">/</span> <span class=\"token number\">2</span> <span class=\"token operator\">&lt;&lt;</span> std<span class=\"token punctuation\">:</span><span class=\"token punctuation\">:</span>endl<span class=\"token punctuation\">;</span>\n\n\t<span class=\"token keyword\">return</span> <span class=\"token number\">0</span><span class=\"token punctuation\">;</span>\n<span class=\"token punctuation\">}</span></code></pre></div>\n<h3>References</h3>\n<p><a href=\"https://m.blog.naver.com/PostView.nhn?blogId=junhyuk7272&#x26;logNo=221247061276&#x26;proxyReferer=https:%2F%2Fwww.google.com%2F\">https://m.blog.naver.com/PostView.nhn?blogId=junhyuk7272&#x26;logNo=221247061276&#x26;proxyReferer=https:%2F%2Fwww.google.com%2F</a><br>\n<a href=\"https://bhsmath.tistory.com/17\">https://bhsmath.tistory.com/17</a><br>\n<a href=\"https://j1w2k3.tistory.com/434\">https://j1w2k3.tistory.com/434</a></p>","fields":{"tagSlugs":["/tags/백준/","/tags/algorithm/"],"slug":"/posts/baekjoons/2355/"},"frontmatter":{"title":"[백준] 2355 : 시그마","tags":["백준","Algorithm"],"date":"2020-05-10","description":"백준 2355번 문제 : 시그마"}}},"pageContext":{"slug":"/posts/baekjoons/2355/"}}