The Runtime Theory
mediumLeetCode#heap#quickselect

Kth Largest Element in an Array

Return the kth largest value including duplicates, without requiring a full sort.

The Runtime Theory Team25 min read
Solve it

Solving happens on the judge — come back and mark it done

Sample cases

innums=[3,2,1,5,6,4], k=2

out5

innums=[3,2,3,1,2,4,5,5,6], k=4

out4

innums=[1], k=1

out1

Return the kth largest value including duplicates, without requiring a full sort.

A good solution should

  • State the invariant or decision rule that makes the approach correct.
  • Explain the time and space complexity in terms of the input sizes and required output.
  • Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.

Reasoning prompt

Compare a size-k min-heap with quickselect. Include duplicate values and state expected versus worst-case complexity.

Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.

More practice in this topic

hard · heapFind Median from Data Streammedium · heapK Closest Points to Originmedium · heapFind K Pairs with Smallest Sums

One dispatch a week

The trace behind each problem, the tradeoff that explains it, and one technical dispatch per week — no noise.

One technical dispatch per week. No noise.

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