Contains Duplicate, solved four ways

Try:
CALL
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Code

The highlighted line runs next. The pill shows the live values in the running call.

Cost

Work done so far, and how the four solutions compare

Array

Arrows mark the positions being compared

Keyboard: ← → step, Space play or pause. Up to 12 numbers; switching solution keeps the input. Try "dup at start" in each mode: the brute force and hash set stop at once, sorting still pays for the sort, and the set-length version still reads everything.