Introduction to Reading Notes algorithms quick sorting quicksort uses the last element as the marker

Quick sorting is the most common sorting method in practical programming applications.

He has excellent performance.

The worst case time complexity is O (n square meters)

The average time complexity is O (n logn) and has a very small coefficient.

And the space complexity is very small, that is, O (n)

But thisAlgorithmIt is also difficult to understand...

The following is a quick algorithm that uses the last element as the token.

 Using  System;
  Using  System. Collections. Generic;
  Using  System. LINQ;
  Using  System. text;
  Using  System. runtime. interopservices;

 Namespace  Introducetoalgorithm
{

  Public     Class  Quicksort
{
  Public     Void  Sort (  Int  [],  Int  Startindex  =     1 ,  Int  Endindex  =     -  1  )
{
  If  (Endindex  =     -  1  )
{
Endindex  = A. length;
}
  If  (Startindex  <  Endindex)
{
  Int  Q  =  Partition (A, startindex, endindex );

Sort (A, startindex, Q  -     1  );
Sort (A, Q  +    1  , Endindex );
}
}

  Public     Int  Partition (  Int  [],  Int  Startindex,  Int  Endindex)
{
  Int  X  =  A [endindex -     1  ];
  Int  I  =  Startindex  -     1  ;

  For  (  Int  J  =  Startindex; j <=  Endindex  -     1  ; J  ++  )
{
  If  (A [J  -     1  ]  <=  X)
{
I  = I  +     1  ;
Exchange (A, I  -     1  , J  -     1  );
}
  //  A. Print ();  
 }
Exchange (A, I, endindex  -     1  );
  //  A. Print ();  
    Return  I  +     1  ;


}

  Public    Void  Exchange (  Int  [],  Int  I,  Int  I2)
{
  Int  Val  =  A [I];
A [I]  =  A [I2];
A [I2]  = Val;
}
}

} 

PS: this algorithm is hard to understand when it is implemented...CodeSee... although there are few codes