Array Algorithms and Techniques

Arrays are where most coding interviews begin, and where the highest-leverage techniques live. Two pointers, sliding window and prefix sums between them turn a large share of quadratic brute-force solutions into linear ones, which is usually the entire difference between a passing and a failing answer.

The visualizers matter more here than almost anywhere else, because these techniques are defined by index movement. Watching a left pointer advance only when a constraint breaks makes the sliding window rule obvious in a way that reading the loop condition does not. Once these are solid, the same techniques reappear as named patterns in the interview pattern library.