Create 1206-design-skiplist.js

Author: everthis

1206-design-skiplist.js

@@ -0,0 +1,82 @@
+const Skiplist = function () {
+  this.maxLvl = ~~Math.log2(20000)
+  this.levels = [...Array(this.maxLvl)].map(() => new Node(-1))
+  for (let i = this.maxLvl - 1; i > 0; i--) {
+    this.levels[i].down = this.levels[i - 1]
+  }
+  this.head = this.levels[this.maxLvl - 1]
+}
+
+/**
+ * @param {number} target
+ * @return {boolean}
+ */
+Skiplist.prototype.search = function (target) {
+  const pre = this.iter(target)
+  return !pre[0].next ? false : pre[0].next.val === target
+}
+
+Skiplist.prototype.iter = function (target) {
+  let cur = this.head
+  const pre = []
+  for (let i = this.maxLvl - 1; i >= 0; i--) {
+    while (cur.next && cur.next.val < target) cur = cur.next
+    pre[i] = cur
+    cur = cur.down
+  }
+  return pre
+}
+
+/**
+ * @param {number} num
+ * @return {void}
+ */
+Skiplist.prototype.add = function (num) {
+  const pre = this.iter(num)
+  const lvs = decideLevels(this.maxLvl)
+  for (let i = 0; i < lvs; i++) {
+    const next = pre[i].next
+    pre[i].next = new Node(num)
+    pre[i].next.next = next
+    if (i > 0) pre[i].next.down = pre[i - 1].next
+  }
+}
+
+/**
+ * @param {number} num
+ * @return {boolean}
+ */
+Skiplist.prototype.erase = function (num) {
+  const pre = this.iter(num)
+  let ret
+  if (!pre[0].next || pre[0].next.val !== num) return false
+  for (let i = this.maxLvl - 1; i >= 0; i--) {
+    if (pre[i].next && pre[i].next.val === num) {
+      const toBeDeleted = pre[i].next
+      pre[i].next = toBeDeleted.next
+      toBeDeleted.next = null
+      toBeDeleted.down = null
+    }
+  }
+  return true
+}
+
+/**
+ * Your Skiplist object will be instantiated and called as such:
+ * var obj = new Skiplist()
+ * var param_1 = obj.search(target)
+ * obj.add(num)
+ * var param_3 = obj.erase(num)
+ */
+
+const decideLevels = (max) => {
+  let ans = 1
+  while (Math.random() > 0.5 && ans < max) ans++
+  return ans
+}
+
+const Node = function (val) {
+  this.val = val
+  this.next = null
+  this.down = null
+}