Hash Set Pattern — LeetCode #217: Contains Duplicate
The article explains the hash set pattern to solve LeetCode problem #217, which determines if an array contains duplicate values. It compares a brute force O(n²) approach with a more efficient O(n) solution using a hash set to track seen elements. The key insight is rephrasing the problem from checking all pairs to asking whether each element has been previously encountered.
- ▪The problem asks to return true if any value in an integer array appears at least twice.
- ▪A brute force solution uses nested loops with O(n²) time complexity, while a hash set approach reduces it to O(n) time.
- ▪The hash set solution checks for each element whether it has already been seen, enabling early termination upon finding a duplicate.
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| Original publisher | DEV.to (Top) |
| Canonical URL | https://dev.to/yash_gandhi_b0979f0105433/hash-set-pattern-leetcode-217-contains-duplicate-4oef |
| Publication time | Sun, 17 May 2026 06:15:35 +0000 |
| Retrieval time | 2026-05-17T06:33:59.083Z |
| Last seen | 2026-05-17T06:33:59.083Z |
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| Retrieval / RAG | May the content be exposed for third-party retrieval-augmented generation? | Not asserted |
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Basis: Derived from the published RSS/Atom feed. Contact: [email protected]. Reviewed: 2026-07-24.
Opening excerpt (first ~120 words) tap to expand
try { if(localStorage) { let currentUser = localStorage.getItem('current_user'); if (currentUser) { currentUser = JSON.parse(currentUser); if (currentUser.id === 3827782) { document.getElementById('article-show-container').classList.add('current-user-is-article-author'); } } } } catch (e) { console.error(e); } Yash Gandhi Posted on May 17 Hash Set Pattern — LeetCode #217: Contains Duplicate #leetcode #dsa #typescript #python LeetCode Patterns (3 Part Series) 1 Loop Invariants Part 1 — The One Concept That Makes Algorithms Click 2 Running State Pattern — LeetCode #1480: Running Sum of 1D Array 3 Hash Set Pattern — LeetCode #217: Contains Duplicate Prerequisites: Loop Invariants (to understand why this works, not just how) | Running Sum (#1480) (the accumulator pattern this builds on).
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