course schedule solution

Author: yhkee0404

course-schedule/yhkee0404.swift

@@ -0,0 +1,32 @@
+class Solution {
+    func canFinish(_ numCourses: Int, _ prerequisites: [[Int]]) -> Bool {
+        var adj: [[Int]] = Array(repeating: [], count: numCourses)
+        for ab in prerequisites {
+            adj[ab[0]].append(ab[1])
+        }
+        var visited = Array(repeating: 0, count: numCourses)
+        var stack = Array(0..<numCourses)
+        while !stack.isEmpty {
+            let u = stack.last!
+            if visited[u] == 2 {
+                stack.removeLast()
+                continue
+            } else if visited[u] == 1 {
+                visited[u] = 2
+                stack.removeLast()
+                continue
+            }
+            visited[u] = 1
+            for v in adj[u] {
+                if visited[v] == 1 {
+                    return false
+                }
+                if visited[v] == 2 {
+                    continue
+                }
+                stack.append(v)
+            }
+        }
+        return true
+    }
+}