Add solution #710

Author: JoshCrozier

0710-random-pick-with-blacklist.js

@@ -0,0 +1,43 @@
+/**
+ * 710. Random Pick with Blacklist
+ * https://leetcode.com/problems/random-pick-with-blacklist/
+ * Difficulty: Hard
+ *
+ * You are given an integer n and an array of unique integers blacklist. Design an algorithm to
+ * pick a random integer in the range [0, n - 1] that is not in blacklist. Any integer that is
+ * in the mentioned range and not in blacklist should be equally likely to be returned.
+ *
+ * Optimize your algorithm such that it minimizes the number of calls to the built-in random
+ * function of your language.
+ *
+ * Implement the Solution class:
+ * - Solution(int n, int[] blacklist) Initializes the object with the integer n and the
+ *   blacklisted integers blacklist.
+ * - int pick() Returns a random integer in the range [0, n - 1] and not in blacklist.
+ */
+
+/**
+ * @param {number} n
+ * @param {number[]} blacklist
+ */
+var Solution = function(n, blacklist) {
+  this.size = n - blacklist.length;
+  this.mapping = new Map();
+  blacklist = new Set(blacklist);
+
+  let last = n - 1;
+  for (const b of blacklist) {
+    if (b < this.size) {
+      while (blacklist.has(last)) last--;
+      this.mapping.set(b, last--);
+    }
+  }
+};
+
+/**
+ * @return {number}
+ */
+Solution.prototype.pick = function() {
+  const index = Math.floor(Math.random() * this.size);
+  return this.mapping.get(index) ?? index;
+};

README.md

@@ -536,6 +536,7 @@
 705|[Design HashSet](./0705-design-hashset.js)|Easy|
 706|[Design HashMap](./0706-design-hashmap.js)|Easy|
 707|[Design Linked List](./0707-design-linked-list.js)|Medium|
+710|[Random Pick with Blacklist](./0710-random-pick-with-blacklist.js)|Hard|
 713|[Subarray Product Less Than K](./0713-subarray-product-less-than-k.js)|Medium|
 714|[Best Time to Buy and Sell Stock with Transaction Fee](./0714-best-time-to-buy-and-sell-stock-with-transaction-fee.js)|Medium|
 717|[1-bit and 2-bit Characters](./0717-1-bit-and-2-bit-characters.js)|Easy|