The Runtime Theory
easyLeetCode#hash-set#duplicates

Contains Duplicate

Decide whether any value occurs more than once, and compare a set-based solution with sorting the input.

The Runtime Theory Team25 min read
Solve it

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

Sample cases

innums=[1,2,3,1]

outtrue

innums=[1,2,3,4]

outfalse

innums=[]

outfalse

Decide whether any value occurs more than once, and compare a set-based solution with sorting the input.

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

Explain whether your implementation mutates the input and why the expected-time guarantee of a hash set is not a worst-case guarantee.

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

medium · arraysEncode and Decode a List of Stringsmedium · arraysGroup Anagramsmedium · arraysLongest Consecutive Sequence

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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