Interactive field notes

Challenges

Step-through visual walkthroughs for the classic interview problems — pick one and watch the idea build up, figure by figure.

01

All challenges

7 problems
EasyLC 1●

Two Sum

Brute-force every pair, then the one-pass hash map that makes the inner search vanish.

Array · Hash Tableopen →
EasyLC 27●

Remove Element

Pack the survivors to the front with a write pointer — plus the swap-from-end variant for rare removals.

Array · Two Pointersopen →
EasyLC 88●

Merge Sorted Array

Merge two sorted arrays in place by filling the empty tail from the back — no conflicts, no copy.

Array · Two Pointersopen →
MediumLC 80●

Remove Duplicates II

Keep at most two of each value in a sorted array, in a single in-place pass.

Array · Two Pointersopen →
EasyLC 1071

GCD of Strings

The largest string that tiles both — the Euclidean GCD trick, reimagined on text.

Strings · Mathopen →
MediumLC 2542

Maximum Subsequence Score

Maximize sum × min by sorting on the minimum and sweeping with a running heap.

Greedy · Heapopen →
Medium

Permit Streaks

Counting the subarrays that sum to a target — prefix sums meet a frequency map.

Prefix Sums · Hash Tableopen →