Thread: two algorithm problems

  1. #1
    Registered User axon's Avatar
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    two algorithm problems

    hey all, its nearing the end of semester and my professor assigned a couple extra credit problems. I'm posting to of which I haven't given much thought to yet, because I think they are the toughest ones.

    What I'm looking for from you guys is suggestions for the solution, thanks.

    1. You are given an array of n distinct numbers a1, a2,...an which you are to sort. You are given the additional information that the array is already "d-nearly sorted"; this means that the position of each number in the given array is no more that distance d from its position in the sorted array. For instance, if an array is "0-nearly sorted", it is in fact sorted; if an array is "(n-1)-nearly sorted", then you have the traditional sorting problem. Devise an algorithm that sorts a d-nearly sorted array in O(n logd) time.

    2. You are given a set of n horizontal line segments {(l1,r1),(l2,r2), ...(ln,rn)" where li and ri give the leftmost and rightmost points on the i'th line segment. Devise an O(n logn) time algorithm to find a point x of maximum overlap among n line segments (a point x which is "covered" by a maximum number of segments).

    any ideas appreciated.

    some entropy with that sink? entropysink.com

    there are two cardinal sins from which all others spring: Impatience and Laziness. - franz kafka

  2. #2
    Redundantly Redundant RoD's Avatar
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    hmmm

    ttt

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    Uhmm, you've tried bubble sort algorithm with array?

  4. #4
    Registered User Codeplug's Avatar
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    Quote Originally Posted by eifersucht
    Uhmm, you've tried bubble sort algorithm with array?
    (n^2) > (n log d)

    ...

    Duh!!

    gg

  5. #5
    Registered User axon's Avatar
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    the only idea I have for part 1 is a modified version of quicksort

    some entropy with that sink? entropysink.com

    there are two cardinal sins from which all others spring: Impatience and Laziness. - franz kafka

  6. #6
    and the hat of int overfl Salem's Avatar
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    In response to your other thread, how about http://nist.gov/dads/
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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