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45 lines
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45 lines
2.1 KiB
HTML
<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>
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<ul>
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<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>
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</ul>
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<p>Return <em>the ordering of courses you should take to finish all courses</em>. If there are many valid answers, return <strong>any</strong> of them. If it is impossible to finish all courses, return <strong>an empty array</strong>.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0]]
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<strong>Output:</strong> [0,1]
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<strong>Explanation:</strong> There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0,1].
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> numCourses = 4, prerequisites = [[1,0],[2,0],[3,1],[3,2]]
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<strong>Output:</strong> [0,2,1,3]
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<strong>Explanation:</strong> There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0.
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So one correct course order is [0,1,2,3]. Another correct ordering is [0,2,1,3].
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> numCourses = 1, prerequisites = []
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<strong>Output:</strong> [0]
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= numCourses <= 2000</code></li>
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<li><code>0 <= prerequisites.length <= numCourses * (numCourses - 1)</code></li>
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<li><code>prerequisites[i].length == 2</code></li>
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<li><code>0 <= a<sub>i</sub>, b<sub>i</sub> < numCourses</code></li>
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<li><code>a<sub>i</sub> != b<sub>i</sub></code></li>
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<li>All the pairs <code>[a<sub>i</sub>, b<sub>i</sub>]</code> are <strong>distinct</strong>.</li>
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</ul>
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