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Thread: best sorting algorithm

  1. #1 best sorting algorithm 
    New Member
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    Jun 2013
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    Hi everyone!

    I do have some urgent questions about sorting algorithms, could you guys please help me?

    We have learnt the following algorithms:
    SelectionSort
    BubbleSort
    InsertionSort
    QuickSort
    MergeSort
    HeapSort

    These are my questions:
    1) I know quicksort has in the avarage case a time complexity of nlog(n), mergesort always has nlog(n) and heapsort also always have nlog(n)
    But for sorting big data, which of these algorithms is the fastest? Because their time complexity is the same..?

    2) For sorting an array which elements are already sorted for a big part, what is the fastest algoritm? I was thinking about insertion sort, but i'm not quite sure..

    3) For an array which is sorted from high to low, what is the fastest algorithm to sort it from low to high?

    Thank you,
    John


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  3. #2  
    Forum Ph.D.
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    For 3) Start from the top and swap with bottom and move in (top and bottom) one step at a time, repeat till you reach the middle.


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  4. #3  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
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    Sort speeds can be affected by many things, including the coding language it is written in and the data types you are sorting.
    The best way to find out which is the fastest algorithm is to create some test data and try each sorting method in turn.

    This page
    Why is quicksort better than other sorting algorithms in practice? - Computer Science Stack Exchange
    goes into a lot of the detail about sort speeds.
    I used to have a link to a really good explanation of each different sorting method, but I appear to have lost it.

    Hopefully that will give you enough information to answer your questions.
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