solve: course schedule

Author: wogha95

course-schedule/wogha95.js

@@ -0,0 +1,49 @@
+/**
+ * TC: O(V + E)
+ * SC: O(V + E)
+ * N: numCourses(all of vertex), P: prerequisites(all of edge)
+ */
+
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+var canFinish = function (numCourses, prerequisites) {
+  const STEP = {
+    before: 0,
+    ing: 1,
+    after: 2,
+  };
+  const stepBoard = Array.from({ length: numCourses }, () => STEP.before);
+  const board = Array.from({ length: numCourses }, () => []);
+
+  for (const [a, b] of prerequisites) {
+    board[a].push(b);
+  }
+
+  for (let index = 0; index < numCourses; index++) {
+    if (isCycle(index)) {
+      return false;
+    }
+  }
+  return true;
+
+  function isCycle(current) {
+    if (stepBoard[current] === STEP.end) {
+      return false;
+    }
+    if (stepBoard[current] === STEP.ing) {
+      return true;
+    }
+
+    stepBoard[current] = STEP.ing;
+    for (const next of board[current]) {
+      if (isCycle(next)) {
+        return true;
+      }
+    }
+    stepBoard[current] = STEP.end;
+    return false;
+  }
+};