## Design - 380. Insert Delete GetRandom O(1)

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380. 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();
``````

go：

``````type RandomizedSet struct {
m map[int]int
arr []int
}

/** Initialize your data structure here. */
func Constructor() RandomizedSet {
return RandomizedSet{
m : make(map[int]int),
arr : make([]int, 0),
}
}

/** 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.m[val]; ok {
return false
}

this.m[val] = len(this.arr)
this.arr = append(this.arr, val)

return true
}

/** Removes a value from the set. Returns true if the set contained the specified element. */
func (this *RandomizedSet) Remove(val int) bool {
index, ok := this.m[val]
if !ok {
return false
}

lastVal := this.arr[len(this.arr) - 1]
if val != lastVal {
this.arr[index] = lastVal
this.m[lastVal] = index
}
// 移除最后一个元素，实现O(1)删除
this.arr = this.arr[:len(this.arr)-1]
delete(this.m, val)
return true
}

/** Get a random element from the set. */
func (this *RandomizedSet) GetRandom() int {
index := rand.Intn(len(this.arr))
return this.arr[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();
*/
``````