Leetcode - Insert Delete GetRandom O(1)

https://leetcode.com/problems/insert-delete-getrandom-o1/

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();

import "math/rand"

type RandomizedSet struct {
    hash map[int]int
    arr []int
}


/** Initialize your data structure here. */
func Constructor() RandomizedSet {
    return RandomizedSet{
        hash: map[int]int{},
        arr: []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 {
    if _, ok := this.hash[val]; ok {
        return false
    }
    this.arr = append(this.arr, val)
    this.hash[val] = len(this.arr)-1
    return true
}


/** Removes a value from the set. Returns true if the set contained the specified element. */
func (this *RandomizedSet) Remove(val int) bool {
    p, ok := this.hash[val]
    if !ok {
        return false
    }
    if p != len(this.arr)-1 {
        this.hash[this.arr[len(this.arr)-1]] = p
        this.arr[p] = this.arr[len(this.arr)-1]
    }
    this.arr = this.arr[:len(this.arr)-1]
    delete(this.hash, val)
    return true
}


/** Get a random element from the set. */
func (this *RandomizedSet) GetRandom() int {
    idx := rand.Int() % len(this.arr)
    return this.arr[idx]
}


/**
 * 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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