Arrays and Strings Tutorial
Master array and string problems in Python: two pointers, sliding window, prefix sums and Unicode-safe text handling
Beginner to Intermediate4 lessonsabout 21 min of reading
Arrays and strings are the raw material of most coding interviews and a large share of real programs: sensor logs, price lists, text fields, CSV lines, API payloads. This course is for people who are comfortable with Python loops and functions and want a set of patterns they can reuse instead of rediscovering them on every problem.
You will learn how a Python list behaves in memory and why some operations are cheap and others are not, then four patterns that turn quadratic loops into single passes: the write pointer and two pointers, the sliding window, prefix sums and difference arrays. The last lesson applies them to text, and covers the Unicode and immutability surprises that make Python strings trickier than they look.
The lessons build on each other. Lesson one covers mechanics and two pointers, lesson two adds the sliding window, lesson three precomputes totals with prefix sums, and lesson four moves to strings. Every snippet is complete and was run to produce the output shown. If you want the underlying cost model first, read Data Structures; when you are ready for ordering problems, continue with Sorting Algorithms.
Arrays and Strings lessons
- 1Arrays and Strings: List Mechanics, In-Place Updates, Two PointersUnderstand how Python lists behave as arrays, update them in place with a write pointer, and use two pointers to solve pair and rotation problems.5 min read
- 2Sliding Window Technique in Python: Fixed and Variable WindowsLearn the sliding window technique in Python with fixed and variable windows, a dict-backed window, and the rule that makes shrinking safe.5 min read
- 3Prefix Sums and Difference Arrays in Python: Range Queries and UpdatesUse prefix sums for instant range-sum queries and difference arrays for bulk range updates in Python, plus a hash-map trick for subarray sums.5 min read
- 4Python String Problems: Anagrams, Palindromes, Parsing and UnicodeSolve common Python string problems: group anagrams, check palindromes, parse messy lines, and avoid Unicode and immutability gotchas.6 min read
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