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);
 */