Problem
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 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
|
// 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();
|
Solution
HashMap + Array
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
|
type RandomizedSet struct {
M map[int]int
A []int
}
/** Initialize your data structure here. */
func Constructor() RandomizedSet {
rand.Seed(time.Now().UnixNano())
return RandomizedSet{
M: make(map[int]int,0),
A: 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.A = append(this.A, val)
this.M[val] = len(this.A)-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 {
if _, ok := this.M[val]; !ok {
return false
}
if len(this.A) == 1 {
this.A = []int {}
} else {
z := this.A[len(this.A)-1]
this.A[this.M[val]], this.A[len(this.A)-1] = this.A[len(this.A)-1], this.A[this.M[val]]
this.M[z] = this.M[val]
this.A = this.A[:len(this.A)-1]
}
delete(this.M, val)
return true
}
/** Get a random element from the set. */
func (this *RandomizedSet) GetRandom() int {
k := rand.Intn(len(this.A))
return this.A[k]
}
/**
* 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();
*/
|