Cutting In, and Keeping Only the Last 100: Deques and Ring Buffers

A paid mobile order jumps to the front of the line, a customer at the back gives up and leaves, and a log must keep only its last 100 lines out of a million. Find the line that's cheap at both ends, and the fixed circle of slots that never moves or grows.

Updated

Cheat sheet: Cutting In, and Keeping Only the Last 100: Deques and Ring Buffers
Category
Data Structures
Level
Journeyman
Tags
data structures, Deque (data-structures), Modulo (software-development), Queue (data-structures), Ring Buffer