🌱 DSA (Beginner) · Core Patterns · cozy lesson

Hash Tables & Counting

11 min · 1 min read · no scary math, promise

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def two_sum(a, t):
    m = {}
    for i, x in enumerate(a):
        if t-x in m: return [m[t-x], i]
        m[x] = i

Pattern: counting → Counter, grouping → dict of lists (anagrams by sorted key).

Correct answers earn XP (once each).

1. Two Sum O(n)?

2. Anagram check?

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