The Last Five Readings

The weather display only shows the freshest k readings — old ones fall off the back as new ones arrive. 🌡️

You get the readings in arrival order and the display size k. Feed them through a deque that never grows past k (drop the oldest when full). Print the final display, oldest first, comma-separated.

Example:

Input: readings = [3, 8, 2, 9, 4, 7], k = 3 Output: 9,4,7

Each new reading is appended, and once the deque holds more than 3 the oldest one is dropped. After all six readings arrive, only the freshest three remain: 9, 4, 7.