Given a string of even size, say:

abcdef123456

How would I interleave the two halves, such that the same string would become this:

a1b2c3d4e5f6

I tried attempting to develop an algorithm, but couldn't. Would anybody give me some hints as to how to proceed? I need to do this without creating extra string variables or arrays. One or two variable is fine.

I just don't want a working code (or algorithm), I need to develop an algorithm and prove it correctness mathematically.

java c++ c algorithm math
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