Add solution #210

Author: JoshCrozier

README.md

@@ -190,6 +190,7 @@
 207|[Course Schedule](./0207-course-schedule.js)|Medium|
 208|[Implement Trie (Prefix Tree)](./0208-implement-trie-prefix-tree.js)|Medium|
 209|[Minimum Size Subarray Sum](./0209-minimum-size-subarray-sum.js)|Medium|
+210|[Course Schedule II](./0210-course-schedule-ii.js)|Medium|
 211|[Design Add and Search Words Data Structure](./0211-design-add-and-search-words-data-structure.js)|Medium|
 213|[House Robber II](./0213-house-robber-ii.js)|Medium|
 214|[Shortest Palindrome](./0214-shortest-palindrome.js)|Hard|

solutions/0210-course-schedule-ii.js

@@ -0,0 +1,52 @@
+/**
+ * 210. Course Schedule II
+ * https://leetcode.com/problems/course-schedule-ii/
+ * 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 the ordering of courses you should take to finish all courses. If there are many valid
+ * answers, return any of them. If it is impossible to finish all courses, return an empty array.
+ */
+
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {number[]}
+ */
+var findOrder = function(numCourses, prerequisites) {
+  const graph = Array(numCourses).fill().map(() => []);
+  const seen = new Set();
+  const path = new Set();
+  const result = [];
+
+  prerequisites.forEach(([c, p]) => graph[p].push(c));
+
+  for (let i = 0; i < numCourses; i++) {
+    if (!seen.has(i) && !dfs(i)) {
+      return [];
+    }
+  }
+
+  return result;
+
+  function dfs(course) {
+    if (path.has(course)) return false;
+    if (seen.has(course)) return true;
+
+    path.add(course);
+    for (const c of graph[course]) {
+      if (!dfs(c)) {
+        return false;
+      }
+    }
+    path.delete(course);
+    seen.add(course);
+    result.unshift(course);
+    return true;
+  }
+};