Create swift/0210-course-schedule-ii.swift

swift/0210-course-schedule-ii.swift

@@ -0,0 +1,44 @@
+class Solution {
+    func findOrder(_ numCourses: Int, _ prerequisites: [[Int]]) -> [Int] {
+        var preMap: [Int: [Int]] = [:]
+
+        for i in 0..<numCourses {
+            preMap[i] = []
+        }
+
+        for prerequisite in prerequisites {
+            guard let course = prerequisite.first,
+                  let prereq = prerequisite.last
+            else { continue }
+            preMap[course]?.append(prereq)
+        }
+
+        var stack: [Int] = []
+        var visited = Set<Int>()
+        var cycle = Set<Int>()
+        func dfs(course: Int, visited: inout Set<Int>, cycle: inout Set<Int>, stack: inout [Int]) -> Bool {
+            guard !cycle.contains(course) else { return false }
+            guard !visited.contains(course) else { return true }
+
+            visited.insert(course)
+            cycle.insert(course)
+
+            let prereqs = preMap[course] ?? []
+            for prereq in prereqs {
+                guard dfs(course: prereq, visited: &visited, cycle: &cycle, stack: &stack) else { return false }
+            }
+
+            cycle.remove(course)
+            stack.append(course)
+
+            return true
+        }
+
+        for course in preMap.keys {
+            guard !visited.contains(course) else { continue }
+            guard dfs(course: course, visited: &visited, cycle: &cycle, stack: &stack) else { return [] }
+        }
+
+        return stack.count <= numCourses ? stack : []
+    }
+}