Update 1942-the-number-of-the-smallest-unoccupied-chair.js

Author: everthis

1942-the-number-of-the-smallest-unoccupied-chair.js

@@ -1,3 +1,106 @@
+/**
+ * @param {number[][]} times
+ * @param {number} targetFriend
+ * @return {number}
+ */
+const smallestChair = function(times, targetFriend) {
+  times.forEach((e, i) => e[2] = i)
+  times.sort((a, b) => a[0] - b[0])
+  const pq = new PQ((a, b) => a[1] < b[1])
+  const available = new PQ((a, b) => a < b)
+  const n = times.length
+  for(let i = 0; i < n; i++) {
+    available.push(i)
+  }
+  const seat = available.pop()
+  times[0].push(seat)
+  pq.push(times[0])
+  if(times[0][2] === targetFriend) return seat
+  for(let i = 1; i < n; i++) {
+    const el = times[i]
+    const [s, e, idx] = el
+    while(!pq.isEmpty() && pq.peek()[1] <= s) {
+      const tmp = pq.pop()
+      available.push(tmp[3])
+    }
+    const seat = available.pop()
+    if(targetFriend === idx) return seat
+    el.push(seat)
+    pq.push(el)
+  }
+  
+};
+
+class PQ {
+  constructor(comparator = (a, b) => a > b) {
+    this.heap = []
+    this.top = 0
+    this.comparator = comparator
+  }
+  size() {
+    return this.heap.length
+  }
+  isEmpty() {
+    return this.size() === 0
+  }
+  peek() {
+    return this.heap[this.top]
+  }
+  push(...values) {
+    values.forEach((value) => {
+      this.heap.push(value)
+      this.siftUp()
+    })
+    return this.size()
+  }
+  pop() {
+    const poppedValue = this.peek()
+    const bottom = this.size() - 1
+    if (bottom > this.top) {
+      this.swap(this.top, bottom)
+    }
+    this.heap.pop()
+    this.siftDown()
+    return poppedValue
+  }
+  replace(value) {
+    const replacedValue = this.peek()
+    this.heap[this.top] = value
+    this.siftDown()
+    return replacedValue
+  }
+
+  parent = (i) => ((i + 1) >>> 1) - 1
+  left = (i) => (i << 1) + 1
+  right = (i) => (i + 1) << 1
+  greater = (i, j) => this.comparator(this.heap[i], this.heap[j])
+  swap = (i, j) => ([this.heap[i], this.heap[j]] = [this.heap[j], this.heap[i]])
+  siftUp = () => {
+    let node = this.size() - 1
+    while (node > this.top && this.greater(node, this.parent(node))) {
+      this.swap(node, this.parent(node))
+      node = this.parent(node)
+    }
+  }
+  siftDown = () => {
+    let node = this.top
+    while (
+      (this.left(node) < this.size() && this.greater(this.left(node), node)) ||
+      (this.right(node) < this.size() && this.greater(this.right(node), node))
+    ) {
+      let maxChild =
+        this.right(node) < this.size() &&
+        this.greater(this.right(node), this.left(node))
+          ? this.right(node)
+          : this.left(node)
+      this.swap(node, maxChild)
+      node = maxChild
+    }
+  }
+}
+
+// another
+
 /**
  * @param {number[][]} times
  * @param {number} targetFriend