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mediumDSA

How does a hash table work?

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01

Understand the problem

Explain hashing and collisions.

hash-table
02

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Nudge consolestandby

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03

Study the solution

A hash table maps keys to array indices via a hash function, giving average O(1) insert/lookup. Collisions (two keys hashing to the same bucket) are handled by chaining (linked lists/trees per bucket) or open addressing (probing). Worst case degrades to O(n) with poor hashing.

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04

Read the code

Frequency count with a hash map
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def char_count(s):
    counts = {}                       # dict = hash table
    for c in s:
        counts[c] = counts.get(c, 0) + 1
    return counts

print(char_count("banana"))          # {'b':1,'a':3,'n':2}
05

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