Intervals & Sliding Window

Ripple's coding rounds run live on CoderPad, and the medium-difficulty problems cluster into a few shapes. Two of them share a spine: you are handed a list of ranges or a stream of numbers, and the answer comes from ordering the data and then walking it once. Merging overlapping intervals and counting subarrays under a cost limit both live here. Neither needs an exotic data structure. Both reward the habit Ripple's interviewers watch for: get it correct first, then reach for the optimization and defend why it holds.

The payments framing is not decoration. A settlement engine reconciles overlapping time windows, a billing system rolls up spans that touch, and a risk check scans a stream of transaction costs for a stretch that stays inside a tolerance band. That is why these two archetypes surface here rather than the pure LeetCode restatement. The phone screen leans on the same instinct in miniature. It often paraphrases an easy arithmetic task as a transaction-cost or sell-order calculation, so the muscle you build on the harder versions carries down to the screen.