Add solution #207

Author: JoshCrozier

README.md

@@ -108,6 +108,7 @@
 203|[Remove Linked List Elements](./0203-remove-linked-list-elements.js)|Easy|
 204|[Count Primes](./0204-count-primes.js)|Medium|
 206|[Reverse Linked List](./0206-reverse-linked-list.js)|Easy|
+207|[Course Schedule](./0207-course-schedule.js)|Medium|
 213|[House Robber II](./0213-house-robber-ii.js)|Medium|
 214|[Shortest Palindrome](./0214-shortest-palindrome.js)|Hard|
 215|[Kth Largest Element in an Array](./0215-kth-largest-element-in-an-array.js)|Medium|

solutions/0207-course-schedule.js

@@ -0,0 +1,49 @@
+/**
+ * 207. Course Schedule
+ * https://leetcode.com/problems/course-schedule/
+ * Difficulty: Medium
+ *
+ * There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1.
+ * You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you
+ * must take course bi first if you want to take course ai.
+ *
+ * For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.
+ *
+ * Return true if you can finish all courses. Otherwise, return false.
+ */
+
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+var canFinish = function(numCourses, prerequisites) {
+  const graph = new Map();
+  const seen = new Set();
+
+  prerequisites.forEach(([course, prerequisite]) => {
+    graph.set(course, graph.get(course) || []);
+    graph.get(course).push(prerequisite);
+  });
+
+  function dfs(course) {
+    if (seen.has(course)) {
+      return false;
+    }
+    seen.add(course);
+    for (const prerequisite of graph.get(course) || []) {
+      if (!dfs(prerequisite)) return false;
+    }
+    seen.delete(course);
+    graph.set(course, []);
+    return true;
+  }
+
+  for (let i = 0; i < numCourses; i++) {
+    if (!dfs(i)) {
+      return false;
+    }
+  }
+
+  return true;
+};