{"id":34782,"date":"2024-11-01T09:31:54","date_gmt":"2024-11-01T09:31:54","guid":{"rendered":"http:\/\/atmokpo.com\/w\/?p=34782"},"modified":"2024-11-01T11:26:34","modified_gmt":"2024-11-01T11:26:34","slug":"swift-coding-test-course-stack-and-queue","status":"publish","type":"post","link":"https:\/\/atmokpo.com\/w\/34782\/","title":{"rendered":"Swift Coding Test Course, Stack and Queue"},"content":{"rendered":"<p><body><\/p>\n<h2>Problem Description<\/h2>\n<p>Given an array of integers <code>arr<\/code>, each element in the array is a non-negative integer. For each element, the task is to find the index of the first element to its right that is greater than itself, and create a new array with those indices. If there is no such element, store -1.<\/p>\n<p>For example, if the array is <code>[2, 1, 5, 3, 6, 4]<\/code>, the result will be <code>[2, 1, 1, 1, -1, -1]<\/code>.<\/p>\n<h2>Approach to the Problem<\/h2>\n<p>This problem can be efficiently approached using a stack. By traversing the entire array only once, we can use the stack to solve the issues occurring on the right side of each element. This reduces the time complexity.<\/p>\n<h3>Algorithm Explanation<\/h3>\n<ol>\n<li>Initialize an array <code>result<\/code> to store the results.<\/li>\n<li>Initialize a stack to store indices.<\/li>\n<li>Traverse the array from right to left.<\/li>\n<ul>\n<li>If the current element is greater than the last element in the stack, pop elements from the stack and store values at the corresponding indices in the result array.<\/li>\n<li>If the stack is empty, store <code>-1<\/code> in the result array.<\/li>\n<li>Add the current index to the stack.<\/li>\n<\/ul>\n<li>Return the final result array.<\/li>\n<\/ol>\n<h2>Code Implementation<\/h2>\n<pre><code>func nextGreaterElement(arr: [Int]) -&gt; [Int] {\n        var result = Array(repeating: -1, count: arr.count)\n        var stack: [Int] = []\n\n        for i in (0..<arr.count).reversed() {\n            while !stack.isEmpty &#038;&#038; arr[i] &lt; arr[stack.last!] {\n                result[i] = stack.removeLast()\n            }\n            if stack.isEmpty {\n                result[i] = -1\n            }\n            stack.append(i)\n        }\n        return result\n    }\n\nlet inputArray = [2, 1, 5, 3, 6, 4]\nlet output = nextGreaterElement(arr: inputArray)\nprint(output)  \/\/ Result: [2, 1, 1, 1, -1, -1]\n<\/code><\/pre>\n<h2>Code Explanation<\/h2>\n<p>The code is structured as follows:<\/p>\n<ul>\n<li><code>result<\/code>: The result array is initialized to -1.<\/li>\n<li><code>stack<\/code>: The stack is initialized to store indices.<\/li>\n<li><code>reversed<\/code>: The array is traversed in reverse. This is done to compare each element with the elements to its right.<\/li>\n<li>Using the pop operation from the stack to find elements greater than itself.<\/li>\n<li>Updating the result array with the found index and adding the current index to the stack.<\/li>\n<\/ul>\n<h2>Time Complexity<\/h2>\n<p>This algorithm adds and removes each element from the stack only once, thus the time complexity is <code>O(n)<\/code>. This is very efficient.<\/p>\n<h2>Conclusion<\/h2>\n<p>In this lecture, we learned how to efficiently solve the given problem using a stack. Stacks and queues are data structures that often appear in various coding interview problems. Therefore, understanding and utilizing these two data structures is essential.<\/p>\n<p>By solving this problem, try to develop your own problem-solving approach and attempt various problems. More problems related to stacks and queues will be covered later.<\/p>\n<p><\/body><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Problem Description Given an array of integers arr, each element in the array is a non-negative integer. For each element, the task is to find the index of the first element to its right that is greater than itself, and create a new array with those indices. If there is no such element, store -1. &hellip; <a href=\"https:\/\/atmokpo.com\/w\/34782\/\" class=\"more-link\">\ub354 \ubcf4\uae30<span class=\"screen-reader-text\"> &#8220;Swift Coding Test Course, Stack and Queue&#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":[129],"tags":[],"class_list":["post-34782","post","type-post","status-publish","format-standard","hentry","category-swift-coding-test"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.2 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Swift Coding Test Course, Stack and Queue - \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\/34782\/\" \/>\n<meta property=\"og:locale\" content=\"ko_KR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Swift Coding Test Course, Stack and Queue - \ub77c\uc774\ube0c\uc2a4\ub9c8\ud2b8\" \/>\n<meta property=\"og:description\" content=\"Problem Description Given an array of integers arr, each element in the array is a non-negative integer. 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