; 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 &nbsp; <b> ''N'' </b> &nbsp; sources.
: Common algorithm: same as above, but keep buffered items and their source descriptors in a [[heap]].


Assume streams are very big. You must not suck them whole in the memory, but read them as streams.
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