2336. Smallest Number in Infinite Set

Medium
You have a set which contains all positive integers [1, 2, 3, 4, 5, ...].
Implement the SmallestInfiniteSet class:
  • SmallestInfiniteSet() Initializes the SmallestInfiniteSet object to contain all positive integers.
  • int popSmallest() Removes and returns the smallest integer contained in the infinite set.
  • void addBack(int num) Adds a positive integer num back into the infinite set, if it is not already in the infinite set.
Example 1:
Input
["SmallestInfiniteSet", "addBack", "popSmallest", "popSmallest", "popSmallest", "addBack", "popSmallest", "popSmallest", "popSmallest"]
[[], [2], [], [], [], [1], [], [], []]
Output
[null, null, 1, 2, 3, null, 1, 4, 5]
​
Explanation
SmallestInfiniteSet smallestInfiniteSet = new SmallestInfiniteSet();
smallestInfiniteSet.addBack(2); // 2 is already in the set, so no change is made.
smallestInfiniteSet.popSmallest(); // return 1, since 1 is the smallest number, and remove it from the set.
smallestInfiniteSet.popSmallest(); // return 2, and remove it from the set.
smallestInfiniteSet.popSmallest(); // return 3, and remove it from the set.
smallestInfiniteSet.addBack(1); // 1 is added back to the set.
smallestInfiniteSet.popSmallest(); // return 1, since 1 was added back to the set and
// is the smallest number, and remove it from the set.
smallestInfiniteSet.popSmallest(); // return 4, and remove it from the set.
smallestInfiniteSet.popSmallest(); // return 5, and remove it from the set.
Constraints:
  • 1 <= num <= 1000
  • At most 1000 calls will be made in total to popSmallest and addBack.

解題

type SmallestInfiniteSet struct {
smallest int
arr []bool
}
​
​
func Constructor() SmallestInfiniteSet {
arr := make([]bool, 1001)
for i:=1;i<1001; i++ {
arr[i] = true
}
​
return SmallestInfiniteSet{ smallest: 1, arr: arr }
}
​
​
func (this *SmallestInfiniteSet) PopSmallest() int {
this.arr[this.smallest] = false
ans := this.smallest
​
for i:=this.smallest+1; i<1001; i++ {
if this.arr[i] {
this.smallest = i
break
}
}
​
return ans
}
​
​
func (this *SmallestInfiniteSet) AddBack(num int) {
this.arr[num] = true
if num < this.smallest {
this.smallest = num
}
}
​
​
/**
* Your SmallestInfiniteSet object will be instantiated and called as such:
* obj := Constructor();
* param_1 := obj.PopSmallest();
* obj.AddBack(num);
*/