Question: about quicksort

June 01 2014 taro 110

0

Dear people in Mapleprimes,

I calculated the following Quick Sort algorithm.

 

restart;
quicksort:=proc(A::array(1,numeric),
m::integer, n::integer) 
local partition, p;

partition:=proc(m,n)
i:=m;
j:=n;
x:=A[j];
while i<j do
if A[i]>x then
A[j]:=A[i];
j:=j-1;
A[i]:=A[j];
else
i:=i+1;
end if;
end do;
A[j]:=x;
p:=j;

end proc:

if m<n then
p:=partition(m,n);
quicksort(A,m,p-1);
quicksort(A,p+1,n);
end if;
eval(A);
end proc:

trace(quicksort);

a:=array([2,4,1,5,3]);

quicksort(a,1,5);

 

Then, in the answer, there was a sentence that

{--> enter , quicksort, , args = , a, , , 2, , , 2

........................

{--> enter , quicksort, , args = , a, , , 4, , , 5

I could understand the reason of the "{--> enter , quicksort, , args = , a, , , 2, , , 2," 

but, I could not understand why 4, , , 5 could appear here. I think there is no reason why n that is the number at 5 

increased from 2 to 5. I thought n continues to be 2.

I hope you will give me some hint for this understanding.

 

I thought it with a lot of time. And, I don't know whether this place is an appropriate place to ask this question.

But, I will be very glad if you teach me some of this.

 

Best wishes.

 

taro

 

 

 

 

 

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