addition / recursion problem
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Thread: addition / recursion problem

  1. #1
    Senior Member
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    addition / recursion problem

    If you wanted to add all numbers together from 1 to x (ex. 1+2+3+4+5...x) what is the best way? Mathmatically there are ways easier than adding them all up in order, but I am curious about the programming side. Are there better ways to do this problem besides the obvious answers of a) one loop that takes forever or b) the recursion solution?

  2. #2
    Senior Member roswell1329's Avatar
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    Jan 2002
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    Not that you should listen to me (I seem to have a problem with Basic Algebra), but I think this will work:

    ((n + 1) / 2) * ((n - 1) + 1)

    or just:

    ((n + 1) / 2) * n

    Incidentally, this should work for a consecutive series between any two numbers. Just replace the inner 1's with the smaller number. For example:

    To add the series 4+5+6+7+8+9+10, the equation would be:

    ((10+4) / 2) * ((10 - 4) + 1)

    Which should equal 49...the same answer to 4+5+6+7+8+9+10. Again, I think this will always work, but I'm not sure.

    The algebraic equation to add all numbers between x and n:

    ((n + x) / 2) * ((n - x) + 1)
    /* You are not expected to understand this. */

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