QuickSort and Hoare Partition

Question

I have a hard time translating QuickSort with Hoare partitioning into C code, and can\'t find out why. The code I\'m using is shown below:

void QuickSort(in         


        

Answer 1

You last C code works. But it's not intuitive. And now I'm studying CLRS luckily. In my opinion, The pseudocode of CLRS is wrong.(At 2e) At last, I find that it would be right if changing a place.

 Hoare-Partition (A, p, r)
 x ← A[p]
     i ← p − 1
     j ← r + 1
 while  TRUE
        repeat   j ←  j − 1
            until     A[j] ≤ x
    repeat   i ←  i + 1
            until     A[i] ≥ x
    if  i < j
              exchange  A[i] ↔ A[j]
    else  
              exchnage  A[r] ↔ A[i]  
              return   i

Yes, Add a exchange A[r] ↔ A[i] can make it works. Why? Because A[i] is now bigger than A[r] OR i == r. So We must exchange to guarantee the feature of a partition.