The order that works
If your placement season starts in three months, follow this path. Short on time? Do the bold steps first: core patterns, trees, aptitude and SQL.
Foundations
Get fluent with arrays, strings and loops before patterns. Read the OS and DBMS notes alongside — they are free and come up in every technical interview.
Core patterns
Hashing, two pointers, sliding window, stacks and binary search. Solve the NeetCode problems first, then the story versions to practise reading long, wordy questions like the ones in online tests.
Aptitude & SQL warm-ups
Twenty minutes a day: one aptitude practice set and a few SQL questions. Online assessments filter on these before anyone looks at your code.
Linked lists, trees and heaps
Pointer manipulation and recursion. Trees are the most-asked topic in product-company interviews, so do every problem here.
Backtracking, graphs and greedy
BFS, DFS, topological sort and union-find, plus the greedy and interval problems that show up as the 'hard' question in OAs.
Dynamic programming
From recursion to memoisation to tabulation. Start with 1-D, then grids and strings.
System design & ML (role-dependent)
For SDE roles at product companies, learn the building blocks and two or three case studies. For data / ML roles, the ML module covers the math and the interview questions.
Mocks and revision
Full-length timed aptitude mocks, the SQL exam-level questions and a second pass through the story problems marked Hard.