Find the Kth Smallest/Largest Element in an Array

Objective: Given an array of integers. find the Kth Smallest/largest element in the array.

Example:

int[] A = { 1, 2, 10, 20, 40, 32, 44, 51, 6 };

K=4. 4th smallest element in given array: 10

Approach: (Kth Smallest Element)

  • Use min-Heap. (Click here to read about Priority Queue).
  • Insert all the elements in the Priority Queue.
  • Extract K elements from the priority queue. The last element (kth) extracted with be the kth smallest element in the array.

Complete Code:

Output:
4th smallest element:10

Note: For kth largest element, implement priority queue for max-Heap.

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If you find anything incorrect or you feel that there is any better approach to solve the above problem, please write comment.
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  • Kamal Chaya

    Is it faster to use hte quickselect algorithm ?

  • eugen_nw

    It is also possible to just sort the input array in ascending order and pick the k-1th element.

    • dogbert82

      That will take O(n) time. Idea here is to not sort the entire array. We can use priority queue or quick sort (i.e. partition only k times) and pivot will land in its correct position.

      • gau246

        Why not just use Arrays.sort() and pick the k-1 th element?

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