Insert Delete GetRandom O(1)

Posted on January 10, 2018November 8, 2019 by braindenny

Design a data structure that supports reqiured operations in O(1) time.

Similar Problems:

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();
 */

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