Coding

2336. Smallest Number in Infinite Set

2023-04-25 2 min read
#Hash Table#Design#Heap (Priority Queue)
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題目敘述

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.

解題思路

Solution

import java.util.PriorityQueue;

class SmallestInfiniteSet {
    PriorityQueue<Integer> pQ;

    public SmallestInfiniteSet() {
        pQ = new PriorityQueue<>();
        for(int i = 1; i <= 1000; i++){
            pQ.add(i);
        }
    }
    
    public int popSmallest() {
        int num = pQ.poll();
        return num;
    }
    
    public void addBack(int num) {
        if(!pQ.contains(num)){
            pQ.add(num);
        }
    }
}

/**
 * Your SmallestInfiniteSet object will be instantiated and called as such:
 * SmallestInfiniteSet obj = new SmallestInfiniteSet();
 * int param_1 = obj.popSmallest();
 * obj.addBack(num);
 */
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