Practice

Can you find the Big-O of real code? 8 questions on loops, logarithms, recursion and space.

8 questions · 10 min · +10 XP

Hash sets, frequency maps, the Two Sum complement trick, prefix sums and Kadane's algorithm.

8 questions · 12 min · +10 XP

Opposite-end pointers, in-place read/write pointers, 3Sum and Container With Most Water.

8 questions · 10 min · +10 XP

Fixed and variable windows, when to shrink, and when the technique does not apply.

8 questions · 10 min · +10 XP

The classic template, lower bound, overflow-safe mid, rotated arrays and binary search on the answer.

8 questions · 10 min · +10 XP

Immutability, StringBuilder, palindromes, reversing words and expand-around-center.

8 questions · 10 min · +10 XP

Reversal, fast and slow pointers, cycle detection, dummy nodes and the gap trick.

8 questions · 10 min · +10 XP

LIFO vs FIFO, matching brackets, RPN, Min Stack and the monotonic stack.

8 questions · 10 min · +10 XP

Base cases, the call stack, recursion trees and the choose–explore–unchoose template.

8 questions · 10 min · +10 XP

Traversals, DFS vs BFS, height, diameter, LCA and validating a BST.

8 questions · 12 min · +10 XP

Min-heap vs max-heap, Top K, Kth largest, merging sorted lists and the two-heap median.

8 questions · 10 min · +10 XP

Adjacency lists, BFS vs DFS, islands, topological sort, union-find and Dijkstra.

8 questions · 12 min · +10 XP

States, recurrences, memoization vs tabulation, coin change, LCS and knapsack.

8 questions · 12 min · +10 XP

When greedy works, interval scheduling, jump game, gas station and partition labels.

8 questions · 10 min · +10 XP

Binary, AND/OR/XOR, shifts, the XOR single-number trick and n & (n − 1).

8 questions · 10 min · +10 XP