{"id":34262,"date":"2024-11-01T09:26:10","date_gmt":"2024-11-01T09:26:10","guid":{"rendered":"http:\/\/atmokpo.com\/w\/?p=34262"},"modified":"2024-11-01T10:57:56","modified_gmt":"2024-11-01T10:57:56","slug":"c-coding-test-course-eulers-pi-2","status":"publish","type":"post","link":"https:\/\/atmokpo.com\/w\/34262\/","title":{"rendered":"C++ Coding Test Course, Euler&#8217;s Pi"},"content":{"rendered":"<p><body><\/p>\n<p>Hello! In this tutorial, we will learn how to solve the Euler&#8217;s Totient Function problem using C++. This problem involves finding the count of integers that are coprime to a given integer n, which are less than or equal to n.<\/p>\n<h2>What is the Euler&#8217;s Totient Function?<\/h2>\n<p>The Euler&#8217;s Totient Function \u03c6(n) is a function that represents the count of integers that are coprime to the number n. For example:<\/p>\n<ul>\n<li>\u03c6(1) = 1 (1 is always coprime with itself)<\/li>\n<li>\u03c6(2) = 1 (The only number less than 2 that is coprime with 2 is 1)<\/li>\n<li>\u03c6(3) = 2 (1 and 2 are coprime with 3)<\/li>\n<li>\u03c6(4) = 2 (1 and 3 are coprime with 4)<\/li>\n<li>\u03c6(5) = 4 (1, 2, 3, 4 are coprime with 5)<\/li>\n<\/ul>\n<h2>Problem Description<\/h2>\n<p>Write an algorithm to calculate the value of \u03c6(n) for a given n. The input will be an integer n (1 \u2264 n \u2264 10<sup>6<\/sup>).<\/p>\n<h3>Example Input<\/h3>\n<pre><code>10<\/code><\/pre>\n<h3>Example Output<\/h3>\n<pre><code>4<\/code><\/pre>\n<p>Explanation: 1, 3, 7, and 9 are coprime with 10.<\/p>\n<h2>Steps to Solve the Problem<\/h2>\n<h3>Step 1: Understand the Properties<\/h3>\n<p>The value of the Euler&#8217;s Totient Function has the following properties:<\/p>\n<ul>\n<li>If p is a prime number, then \u03c6(p) = p &#8211; 1<\/li>\n<li>If p is a prime number, then \u03c6(p<sup>k<\/sup>) = p<sup>k<\/sup> &#8211; p<sup>k-1<\/sup> = p<sup>k<\/sup>(1 &#8211; 1\/p)<\/li>\n<li>If two primes p and q are coprime, then \u03c6(p*q) = \u03c6(p) * \u03c6(q)<\/li>\n<\/ul>\n<h3>Step 2: Use the Sieve of Eratosthenes for Range Calculation<\/h3>\n<p>To find the Euler&#8217;s Totient values for all numbers up to n, we can utilize the Sieve of Eratosthenes method to find composite numbers and calculate the totient values. This method operates with a time complexity of O(n log log n).<\/p>\n<h3>Step 3: Implement the Algorithm<\/h3>\n<p>Here is an implementation in C++ for calculating the Euler&#8217;s Totient Function:<\/p>\n<pre><code>\n#include &lt;iostream&gt;\n#include &lt;vector&gt;\n\nusing namespace std;\n\nvoid eulerTotient(int n, vector&lt;int&gt;&amp; phi) {\n    for (int i = 0; i &lt;= n; i++) {\n        phi[i] = i; \/\/ initialize phi\n    }\n    for (int i = 2; i &lt;= n; i++) {\n        if (phi[i] == i) { \/\/ if i is prime\n            for (int j = i; j &lt;= n; j += i) {\n                phi[j] *= (i - 1); \/\/ multiply by (1 - 1\/p) since prime p is included\n                phi[j] \/= i;\n            }\n        }\n    }\n}\n\nint main() {\n    int n;\n    cout &lt;&lt; \"Please enter the value of n: \";\n    cin &gt;&gt; n;\n\n    vector&lt;int&gt; phi(n + 1);\n    eulerTotient(n, phi);\n\n    cout &lt;&lt; \"\u03c6(\" &lt;&lt; n &lt;&lt; \") = \" &lt;&lt; phi[n] &lt;&lt; endl;\n    return 0;\n}\n    <\/code><\/pre>\n<h3>Step 4: Explanation of the Code<\/h3>\n<p>In the above code:<\/p>\n<ul>\n<li>First, we initialize \u03c6[i] for each number.<\/li>\n<li>Next, we find the prime i and update \u03c6[j] for all multiples j.<\/li>\n<li>Finally, the Euler&#8217;s Totient value for n is stored in \u03c6[n].<\/li>\n<\/ul>\n<h3>Step 5: Performance Improvement<\/h3>\n<p>This algorithm has a performance of O(n log log n), which works efficiently even for the maximum range of 10<sup>6<\/sup>.<\/p>\n<h2>Conclusion<\/h2>\n<p>In this tutorial, we covered how to efficiently calculate the Euler&#8217;s Totient Function using C++. The method utilizing the Sieve of Eratosthenes is fast and useful, and it can also be beneficial for coding tests. Keep studying various algorithms to enhance your coding skills!<\/p>\n<h2>References<\/h2>\n<ul>\n<li><a href=\"https:\/\/en.wikipedia.org\/wiki\/Euler%27s_totient_function\">Euler&#8217;s Totient Function &#8211; Wikipedia<\/a><\/li>\n<li><a href=\"https:\/\/www.geeksforgeeks.org\/eulers-totient-function-set-2-when-n-is-a-product-of-two-primes\/\">GeeksforGeeks &#8211; Euler&#8217;s Totient Function<\/a><\/li>\n<\/ul>\n<p><\/body><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Hello! In this tutorial, we will learn how to solve the Euler&#8217;s Totient Function problem using C++. This problem involves finding the count of integers that are coprime to a given integer n, which are less than or equal to n. What is the Euler&#8217;s Totient Function? The Euler&#8217;s Totient Function \u03c6(n) is a function &hellip; <a href=\"https:\/\/atmokpo.com\/w\/34262\/\" class=\"more-link\">\ub354 \ubcf4\uae30<span class=\"screen-reader-text\"> &#8220;C++ Coding Test Course, Euler&#8217;s Pi&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[111],"tags":[],"class_list":["post-34262","post","type-post","status-publish","format-standard","hentry","category-c-coding-test-tutorials-2"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.2 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>C++ Coding Test Course, Euler&#039;s Pi - \ub77c\uc774\ube0c\uc2a4\ub9c8\ud2b8<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/atmokpo.com\/w\/34262\/\" \/>\n<meta property=\"og:locale\" content=\"ko_KR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"C++ Coding Test Course, Euler&#039;s Pi - \ub77c\uc774\ube0c\uc2a4\ub9c8\ud2b8\" \/>\n<meta property=\"og:description\" content=\"Hello! In this tutorial, we will learn how to solve the Euler&#8217;s Totient Function problem using C++. This problem involves finding the count of integers that are coprime to a given integer n, which are less than or equal to n. What is the Euler&#8217;s Totient Function? 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