1575 articles
Learn how to rotate an n×n matrix 90° clockwise in-place using the elegant transpose-then-reverse trick. Understand the math behind it, see the 4-cell direct rotation alternative, dry-run through a worked example, avoid the four most common mistakes, and get clean Python + JavaScript solutions.
Next Permutation is not just an array problem — it is a test of systematic algorithmic thinking under pressure. Learn why you scan from the right, why you swap with the smallest larger element, and why the suffix is reversed rather than sorted. Includes full visual dry runs, the 4 most common bugs, and Python + JavaScript solutions.
LeetCode 287 eliminates every naive approach through three hard constraints: no array modification, O(1) space, O(n) time. The solution — treating the array as an implicit linked list and running Floyd's tortoise-and-hare cycle detection — is one of the most elegant algorithm mappings in all of DSA. Full proof, visual dry run, Python and JavaScript solutions.
Master Dijkstra's Dutch National Flag algorithm to sort 0s, 1s, and 2s in a single pass with O(1) space. Understand the three-pointer invariants, the critical bug most candidates make, and how this pattern unlocks a family of partition problems.
Insert a new interval into a sorted non-overlapping list and merge any overlaps in a single sweep.