LeetCode: Insert Delete GetRandom O(1) Posted on January 10, 2018July 26, 2020 by braindenny Design a data structure that supports reqiured operations in O(1) time. Similar Problems: CheatSheet: Leetcode For Code Interview CheatSheet: Common Code Problems & Follow-ups Tag: #oodesign, #random Design a data structure that supports all following operations in average O(1) time. insert(val): Inserts an item val to the set if not already present. remove(val): Removes an item val from the set if present. 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(); Github: code.dennyzhang.com Credits To: leetcode.com Leave me comments, if you have better ways to solve. Solution // https://code.dennyzhang.com/insert-delete-getrandom-o1 // Basic Ideas: array // // When deleting, replace it with the last element // // Complexity: Time O(1), Space O(n) import "math/rand" type RandomizedSet struct { m map[int]int l []int } /** Initialize your data structure here. */ func Constructor() RandomizedSet { return RandomizedSet{m:map[int]int{}, l:[]int{}} } /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */ func (this *RandomizedSet) Insert(val int) bool { res := false if _, ok := this.m[val]; !ok { res = true this.m[val] = len(this.l) this.l = append(this.l, val) } return res } /** Removes a value from the set. Returns true if the set contained the specified element. */ func (this *RandomizedSet) Remove(val int) bool { res := false if _, ok := this.m[val]; ok { res = true last_element, index := this.l[len(this.l)-1], this.m[val] this.m[last_element] = index this.l[index] = last_element this.l = this.l[0:len(this.l)-1] delete(this.m, val) } return res } /** Get a random element from the set. */ func (this *RandomizedSet) GetRandom() int { index := rand.Intn(len(this.l)) return this.l[index] } /** * Your RandomizedSet object will be instantiated and called as such: * obj := Constructor(); * param_1 := obj.Insert(val); * param_2 := obj.Remove(val); * param_3 := obj.GetRandom(); */ Post Views: 5