Sorting an array in C

Question

Which is the best sorting technique to sort the following array and if there are duplicates how to handle them   int a   1 3 6 7 1 2     Also which is the best sorting technique of all   void BubbleSort int a    int array size        int i  j  temp      for  i   0  i  lt   array size - 1     i                for  j   0  j  lt  array size - 1 - i    j                         if  a j   gt  a j 1                                 temp   a j 1                   a j 1    a j                   a j    temp

User · Answer

The best sorting technique of all generally depends upon the size of an array  Merge sort can be the best of all as it manages better space and time complexity according to the Big-O algorithm  This suits better for a large array

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I d like to make some changes  In C  you can use the built in qsort command   int compare  const void  a  const void  b       int int a        int   a       int int b        int   b           an easy expression for comparing    return  int a  gt  int b  -  int a  lt  int b      qsort  a  6  sizeof int   compare

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In C  you can use the built in qsort command    int compare  const void  a  const void  b         int int a        int   a         int int b        int   b          if   int a    int b   return 0       else if   int a  lt  int b   return -1       else return 1     qsort  a  6  sizeof int   compare     see  http   www cplusplus com reference clibrary cstdlib qsort     To answer the second part of your question  an optimal  comparison based  sorting algorithm is one that runs with O n log n   comparisons  There are several that have this property  including quick sort  merge sort  heap sort  etc    but which one to use depends on your use case   As a side note  you can sometime do better than O n log n   if you know something about your data - see the wikipedia article on Radix Sort

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Depends  It depends on various things  But in general algorithms using a Divide-and-Conquer   dichotomic approach will perform well for sorting problems as they present interesting average-case complexities   Basics  To understand which algorithms work best  you will need basic knowledge of algorithms complexity and big-O notation  so you can understand how they rate in terms of average case  best case  and worst case scenarios  If required  you d also have to pay attention to the sorting algorithm s stability   For instance  usually an efficient algorithm is quicksort  However  if you give quicksort a perfectly inverted list  then it will perform poorly  a simple selection sort will perform better in that case    Shell-sort would also usually be a good complement to quicksort if you perform a pre-analysis of your list   Have a look at the following  for  advanced searches  using divide and conquer approaches    quicksort shellsort mergesort   And these more straighforward algorithms for less complex ones    bubblesort selection sort insert sort   Further  The above are the usual suspects when getting started  but there are countless others   As pointed out by R  in the comments and by kriss in his answer  you may want to have a look at HeapSort  which provides a theoretically better sorting complexity than a quicksort  but will won t often fare better in practical settings   There are also variants and hybrid algorithms  e g  TimSort

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In your particular case the fastest sort is probably the one described in this answer  It is exactly optimized for an array of 6 ints and uses sorting networks  It is 20 times  measured on x86  faster than library qsort  Sorting networks are optimal for sort of fixed length arrays  As they are a fixed sequence of instructions they can even be implemented easily by hardware   Generally speaking there is many sorting algorithms optimized for some specialized case  The general purpose algorithms like heap sort or quick sort are optimized for in place sorting of an array of items  They yield a complexity of O n log n    n being the number of items to sort    The library function qsort   is very well coded and efficient in terms of complexity  but uses a call to some comparizon function provided by user  and this call has a quite high cost   For sorting very large amount of datas algorithms have also to take care of swapping of data to and from disk  this is the kind of sorts implemented in databases and your best bet if you have such needs is to put datas in some database and use the built in sort

[c] Sorting an array in C?

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