Hashing and maps in Python
Why it matters
Hashing is used for frequency counting, duplicate checks, and lookup optimization.
Problems to practice
- Valid Anagram
- Top K Frequent Elements
- First Non-Repeating Character
- Longest Consecutive Sequence
- Subarray Sum Equals K
Example: counts with dict
freq = {}
for ch in s:
freq[ch] = freq.get(ch, 0) + 1Interview guidance
Use a dictionary when lookup by key dominates the problem.
Can you explain it without the notes?
Hashing and maps in Python
Use your own words. Explain an example and one limitation before checking the explanation.
Check your explanation
Why it matters
Turn this concept into a clear answer.
Practice this conceptAdapted from 18_DSA_PYTHON.md · “3. Hashing and maps in Python”. Examples are study fragments; framework behavior can depend on your version.