Python DSA — Beginner
Start from zero confidence and build it up. Every problem here uses one simple idea — a loop, a list, a dictionary, or a set. No tricks, just fundamentals that stick.
Loop through a list and accumulate a total — the most basic pattern you will use in every program you ever write.
Loop + if condition — filtering with modulo (%). Practice reading each element and deciding whether to count it.
Track a running max in a loop — the pattern behind argmax, leaderboard rankings, and top-N logic.
Same loop pattern as max — practice it in both directions before combining them.
Build a reversed list with a loop or slicing [::-1] — your first look at index manipulation.
Prefix sums — store cumulative totals as you go. This pattern powers analytics and range queries.
Linear search with a counter — lays the groundwork for frequency maps and GROUP BY logic.
Build a filtered list — [x for x in arr if x != val]. List comprehension is a must-know Python pattern.
Track two variables in one pass — extends the max pattern and forces careful edge-case thinking.
Loop over a string character by character — strings are just lists of characters in Python.
split() + reverse + join() — three string methods chained together. The classic string manipulation pattern.
Build a dict with a loop — your introduction to frequency maps (Counter). Used in anagram, substring, and histogram problems.
Frequency dict + max(dict, key=dict.get) — builds directly on count-char-frequency. Two ideas in one problem.
Compare two frequency dicts — your first use of a dict as a comparison tool, not just storage.
Two-pass loop: build frequency map, then find first count-1 char — a clean example of why two passes beats one.
Sum formula trick: expected sum minus actual sum = missing value. Your first O(1) space algorithm.
Use a set to detect the first repeated element — sets give O(1) lookup, making this O(n) overall.
Convert both to sets and use & — your first set operation. Directly models SQL INNER JOIN on IDs.
Two-pointer read-through — advance one pointer only on match. Clean intro to the two-pointer idea.
split() + capitalize() + join() — string pipeline thinking. Finish with a confidence boost problem.