207 js

Author: lazzzis

207/main.js

@@ -0,0 +1,85 @@
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+var canFinish = function(numCourses, prerequisites) {
+  const indegrees = new Array(numCourses).fill(0)
+  const c = Array.from({ length: numCourses }, () => new Set())
+  for (const [from, to] of prerequisites) {
+    ++indegrees[to]
+    c[from].add(to)
+  }
+  const q = new Queue()
+  for (let i = 0; i < numCourses; i++) {
+    if (indegrees[i] === 0) {
+      q.push(i)
+    }
+  }
+  while (!q.empty()) {
+    const cur = q.top()
+    q.pop()
+    for (const to of c[cur]) {
+      --indegrees[to]
+      if (indegrees[to] === 0) {
+        q.push(to)
+      }
+    }
+  }
+  for (let i = 0; i < numCourses; i++) {
+    if (indegrees[i]) {
+      return false
+    }
+  }
+  return true
+};
+
+class Queue {
+  constructor () {
+    this._front = this._back = { val: null, next: null }
+    this._length = 0
+  }
+
+  push (val) {
+    this._back.next = {
+      val,
+      next: null
+    }
+    this._back = this._back.next
+    this._length += 1
+  }
+
+  pop () {
+    if (this._length === 0) {
+      throw new Error('failed to pop: empty queue')
+    }
+    this._length -= 1
+    this._front = this._front.next
+    return this._front.val
+  }
+
+  top () {
+    if (this._length === 0) {
+      throw new Error('Failed to top: empty queue')
+    }
+    return this._front.next.val
+  }
+
+  get length () {
+    return this._length
+  }
+
+  empty () {
+    return this._length === 0
+  }
+
+  clear () {
+    this._front = this._back = { val: null, next: null }
+    this._length = 0
+  }
+}
+
+if (process.env.LZS) {
+  console.log(canFinish(2, [[0, 1], [1, 0]]))
+  console.log(canFinish(2, [[0, 1]]))
+}