mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
synced 2025-01-10 18:48:13 +08:00
188 lines
18 KiB
JSON
188 lines
18 KiB
JSON
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"title": "Course Schedule",
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"content": "<p>There are a total of <code>numCourses</code> courses you have to take, labeled from <code>0</code> to <code>numCourses - 1</code>. You are given an array <code>prerequisites</code> where <code>prerequisites[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> indicates that you <strong>must</strong> take course <code>b<sub>i</sub></code> first if you want to take course <code>a<sub>i</sub></code>.</p>\n\n<ul>\n\t<li>For example, the pair <code>[0, 1]</code>, indicates that to take course <code>0</code> you have to first take course <code>1</code>.</li>\n</ul>\n\n<p>Return <code>true</code> if you can finish all courses. Otherwise, return <code>false</code>.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0]]\n<strong>Output:</strong> true\n<strong>Explanation:</strong> There are a total of 2 courses to take. \nTo take course 1 you should have finished course 0. So it is possible.\n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0],[0,1]]\n<strong>Output:</strong> false\n<strong>Explanation:</strong> There are a total of 2 courses to take. \nTo take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= numCourses <= 10<sup>5</sup></code></li>\n\t<li><code>0 <= prerequisites.length <= 5000</code></li>\n\t<li><code>prerequisites[i].length == 2</code></li>\n\t<li><code>0 <= a<sub>i</sub>, b<sub>i</sub> < numCourses</code></li>\n\t<li>All the pairs prerequisites[i] are <strong>unique</strong>.</li>\n</ul>\n",
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"difficulty": "Medium",
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"exampleTestcases": "2\n[[1,0]]\n2\n[[1,0],[0,1]]",
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"categoryTitle": "Algorithms",
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"name": "Depth-First Search",
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"name": "Topological Sort",
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"code": "# @param {Integer} num_courses\n# @param {Integer[][]} prerequisites\n# @return {Boolean}\ndef can_finish(num_courses, prerequisites)\n \nend",
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"code": "class Solution {\n\n /**\n * @param Integer $numCourses\n * @param Integer[][] $prerequisites\n * @return Boolean\n */\n function canFinish($numCourses, $prerequisites) {\n \n }\n}",
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"code": "(define/contract (can-finish numCourses prerequisites)\n (-> exact-integer? (listof (listof exact-integer?)) boolean?)\n\n )",
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"code": "-spec can_finish(NumCourses :: integer(), Prerequisites :: [[integer()]]) -> boolean().\ncan_finish(NumCourses, Prerequisites) ->\n .",
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"This problem is equivalent to finding if a cycle exists in a directed graph. If a cycle exists, no topological ordering exists and therefore it will be impossible to take all courses.",
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"<a href=\"https://class.coursera.org/algo-003/lecture/52\" target=\"_blank\">Topological Sort via DFS</a> - A great video tutorial (21 minutes) on Coursera explaining the basic concepts of Topological Sort.",
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"Topological sort could also be done via <a href=\"http://en.wikipedia.org/wiki/Topological_sorting#Algorithms\" target=\"_blank\">BFS</a>."
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