LeetCode in Kotlin

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.

Solution

class SmallestInfiniteSet {
    private val set = IntArray(1001)
    private var ptr = 1

    init {
        for (i in 1..1000) {
            set[i] = 1
        }
    }

    fun popSmallest(): Int {
        var `val` = -1
        if (ptr in 1..1000) {
            set[ptr] = 0
            `val` = ptr++
            while (ptr <= 1000 && set[ptr] == 0) {
                ptr++
            }
        }
        return `val`
    }

    fun addBack(num: Int) {
        if (set[num] == 0) {
            set[num] = 1
            if (num < ptr) {
                ptr = num
            }
        }
    }
}

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