国外版

算法题（国外版）/course-schedule.html

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+<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>
+
+<ul>
+	<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>
+</ul>
+
+<p>Return <code>true</code> if you can finish all courses. Otherwise, return <code>false</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0]]
+<strong>Output:</strong> true
+<strong>Explanation:</strong> There are a total of 2 courses to take. 
+To take course 1 you should have finished course 0. So it is possible.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> numCourses = 2, prerequisites = [[1,0],[0,1]]
+<strong>Output:</strong> false
+<strong>Explanation:</strong> There are a total of 2 courses to take. 
+To 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.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= numCourses &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= prerequisites.length &lt;= 5000</code></li>
+	<li><code>prerequisites[i].length == 2</code></li>
+	<li><code>0 &lt;= a<sub>i</sub>, b<sub>i</sub> &lt; numCourses</code></li>
+	<li>All the pairs prerequisites[i] are <strong>unique</strong>.</li>
+</ul>