Insert Delete GetRandom O(1)

README.md

@@ -310,6 +310,7 @@ A collection of JavaScript problems and solutions for studying algorithms.
 - [LFU Cache](src/design/lfu-cache.js)
 - [Min Stack](src/design/min-stack.js)
 - [Max Stack](src/design/max-stack.js)
+- [Insert Delete GetRandom O(1)](src/design/insert-delete-getrandom-o1.js)
 
 ## Author
 

src/design/insert-delete-getrandom-o1.js

@@ -0,0 +1,105 @@
+/**
+ * Insert Delete GetRandom O(1)
+ *
+ * Design a data structure that supports all following operations in average O(1) time.
+ *
+ * 1. insert(val): Inserts an item val to the set if not already present.
+ * 2. remove(val): Removes an item val from the set if present.
+ * 3. getRandom: Returns a random element from current set of elements.
+ *    Each element must have the same probability of being  * returned.
+ *
+ * Example:
+ *
+ * // Init an empty set.
+ * RandomizedSet randomSet = new RandomizedSet();
+ *
+ * // Inserts 1 to the set. Returns true as 1 was inserted successfully.
+ * randomSet.insert(1);
+ *
+ * // Returns false as 2 does not exist in the set.
+ * randomSet.remove(2);
+ *
+ * // Inserts 2 to the set, returns true. Set now contains [1,2].
+ * randomSet.insert(2);
+ *
+ * // getRandom should return either 1 or 2 randomly.
+ * randomSet.getRandom();
+ *
+ * // Removes 1 from the set, returns true. Set now contains [2].
+ * randomSet.remove(1);
+ *
+ * // 2 was already in the set, so return false.
+ * randomSet.insert(2);
+ *
+ * // Since 2 is the only number in the set, getRandom always return 2.
+ * randomSet.getRandom();
+ */
+
+/**
+ * Your RandomizedSet object will be instantiated and called as such:
+ * var obj = Object.create(RandomizedSet).createNew()
+ * var param_1 = obj.insert(val)
+ * var param_2 = obj.remove(val)
+ * var param_3 = obj.getRandom()
+ */
+
+/**
+ * Initialize your data structure here.
+ */
+class RandomizedSet {
+  constructor() {
+    // Stores vals
+    this.nums = [];
+    // Track val's location in nums array
+    this.locs = new Map();
+  }
+
+  /**
+   * Inserts a value to the set. Returns true if the set did not already contain the specified element.
+   * @param {number} val
+   * @return {boolean}
+   */
+  insert(val) {
+    if (this.locs.has(val)) {
+      return false;
+    }
+
+    this.locs.set(val, this.nums.length);
+    this.nums.push(val);
+    return true;
+  }
+
+  /**
+   * Removes a value from the set. Returns true if the set contained the specified element.
+   * @param {number} val
+   * @return {boolean}
+   */
+  remove(val) {
+    if (!this.locs.has(val)) {
+      return false;
+    }
+
+    const loc = this.locs.get(val);
+
+    // The key is to swap the location of val with the last val
+    if (loc !== this.nums.length - 1) {
+      const lastVal = this.nums[this.nums.length - 1];
+      this.nums[loc] = lastVal; // swap in nums
+      this.locs.set(lastVal, loc); // swap in locs
+    }
+
+    this.locs.delete(val);
+    this.nums.pop();
+    return true;
+  }
+
+  /**
+   * Get a random element from the set.
+   * @return {number}
+   */
+  getRandom() {
+    return this.nums[Math.floor(Math.random() * this.nums.length)];
+  }
+}
+
+export { RandomizedSet };