quicksort

I found the following code for finding a pivot for quicksort using median of first, last and middle element: int middle = ( low + high ) / 2; if( a[ middle ].compareTo( a[ low ] ) < 0 ) swapReferences( a, low, middle ); if( a[ high ].compareTo( a[ low ] ) < 0 ) swapReferences( a, low, high ); if( a[ high ].compareTo( a[ middle ] ) < 0 ) swapReferences( a, middle, high ); // Place pivot at position high - 1 swapReferences( a, middle, high - 1 ); Comparable pivot = a[ high - 1 ]; I want to know after finding the median, why is the swap done with index high-1 instead of high? The reason is that

Thanks Doug. Here's the fix: void swap(int& a, int& b) { if (&a == &b) // added this check to ensure the same address is not passed in return; a ^= b; b ^= a; a ^= b; } I am implementing quicksort for fun in C++, and I am using integers for dummy data. I had been using the XOR swapping algorithm to swap two values in place, but I noticed my sort was screwing up. I changed my swapping algorithm and it worked. I added some debugging statements, and found that the XOR swap was doing something weird. I printed the data before and after I swapped it, and this is what it printed: ... swapping -5, -3

For refreshing some Java I tried to implement a quicksort (inplace) algorithm that can sort integer arrays. Following is the code I've got so far. You can call it by sort(a,0,a.length-1) . This code obviously fails (gets into an infinite loop) if both 'pointers' i,j point each to an array entry that have the same values as the pivot. The pivot element v is always the right most of the current partition (the one with the greatest index). But I just cannot figure out how to avoid that, does anyone see a solution? static void sort(int a[], int left, int right) { if (right > left){ int i=left, j

Attempting to learn from doing an implementation of Quicksort, I cannot find out why it's not sorting properly. Using this sequence: 6, 7, 12, 5, 9, 8, 65, 3 It returns this: 3, 5, 7, 8, 9, 65, 12, 6 It seems to sort somewhat, but not all. What have I missed? Here's my code: static void Main(string[] args) { QuickSort qs = new QuickSort(); int[] arr = new int[] { 6, 7, 12, 5, 9, 8, 65, 3 }; foreach (int l in arr) { Console.Write(l + ", "); } int left = 0; int right = arr.Count() - 1; int[] arrr = qs.DoQuickSort(ref arr, left, right); Console.WriteLine("Sorted List: "); foreach (int i in arrr)

I have a custom type Position(x,y,z) ,now I create a ArrayList<Position> , i want to sort this array ordered by the value of z, from small to bigger,how can i do that using Collections.sort or is there any other efficient sorting method? When I try to use public class PositionComparator implements Comparator<Position> { @Override public int compare(Position o1, Position o2) { // TODO Auto-generated method stub return o1.height().compareTo(o2.height()); } } get an error Cannot invoke compareTo(double) on the primitive type double try Collections.sort(SortList, new Comparator<Position>(){ public