Line of Pairs

The rollercoaster seats two — the line boards in pairs, front two together. 🎢

You get the line (front first). Print each riding pair on its own line as name+name, in boarding order. If someone is left alone at the end, print alone:name last.

Example:

Input: line = ["mia", "leo", "kai", "ana", "bo"] Output:

mia+leo
kai+ana
alone:bo

Pairs form front-two-at-a-time (mia+leo, then kai+ana), leaving bo alone since the line has an odd count.