LF.25.K Smallest In Unsorted Array

Find the K smallest numbers in an unsorted integer array A. The returned numbers should be in ascending order.

Assumptions

A is not null
K is >= 0 and smaller than or equal to size of A
Return

an array with size K containing the K smallest numbers in ascending order
Examples

A = {3, 4, 1, 2, 5}, K = 3, the 3 smallest numbers are {1, 2, 3}

 

public int[] kSmallest(int[] array, int k) {
    // Write your solution here
    int[] res = minHeap(array, k);
    return res ;

  }
  //method 1: min heap
  private int[] minHeap(int[] array, int k){
    int[] res = new int[k] ;
    //this is the priority queue
    Queue<Integer> queue = new PriorityQueue<Integer>() ;
    //step1 : offer all items in the queue
    for (int i=0; i<array.length ; i++) {
        queue.offer(array[i]);
    }
    //step 2, poll the k items out
    for (int i=0; i<k; i++) {
        int value = queue.poll();
        res[i] = value;
    }
    return res ;
  }