Stream merge
You are encouraged to solve this task according to the task description, using any language you may know.
Description
2-stream merge
Read two sorted streams of items from external source (e.g. disk, or network), and write one stream of sorted items to external sink.
Common algorithm: keep 1 buffered item from each source, select minimal of them, write it, fetch another item from that stream from which the written item was.
N-stream merge
The same as above, but reading from N sources.
Common solution: same as above, but keep buffered items and their source descriptors in a heap.
Shell
sort --merge source1 source2 sourceN > sink