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#include "quicksort.h"
// Quicksort controller function, it partitions the different pieces of our array.
void quicksort(int *arIntegers, int left, int right)
{
/* cout << "quicksort ([" << arIntegers[0] << ","
<< arIntegers[1] << ","
<< arIntegers[2] << ","
<< arIntegers[3] << ","
<< arIntegers[4] << ","
<< arIntegers[5] << ","
<< arIntegers[6] << "],"
<< left << ","
<< right << ")\n";
*/
if (right > left)
{
int pivotIndex = median3(arIntegers,left,right);
int pivotNewIndex = partition(arIntegers, left, right, pivotIndex);
// Recursive call to quicksort to sort each half.
quicksort(arIntegers, left, pivotNewIndex-1);
quicksort(arIntegers, pivotNewIndex+1, right);
}
}
int median3(int *arIntegers,int left,int right)
{
int center = (left+right)/2;
if(arIntegers[center] < arIntegers[left])
swap(arIntegers[left],arIntegers[center]);
if(arIntegers[right] < arIntegers[left])
swap(arIntegers[left],arIntegers[right]);
if(arIntegers[right] < arIntegers[center])
swap(arIntegers[center],arIntegers[right]);
swap(arIntegers[center],arIntegers[right-1]);
return center;
}
// This function takes an array (or one half an array) and sorts it.
// It then returns a new pivot index number back to quicksort.
int partition(int *arIntegers, int left, int right, int pivot)
{
/* cout << "partition ("<< arIntegers[0] << ","
<< arIntegers[1] << ","
<< arIntegers[2] << ","
<< arIntegers[3] << ","
<< arIntegers[4] << ","
<< arIntegers[5] << ","
<< arIntegers[6] << "],"
<< left << ","
<< right << ")\n";
*/
int pivotValue = arIntegers[pivot];
// Swap it out all the way to the end of the array
// So we know where it always is.
swap(arIntegers[pivot], arIntegers[right]);
int storeIndex = left;
// Move through the array from start to finish comparing each to our
// pivot value (not index, the value that was located at the pivot index)
for (int i = left; i < right; i++)
{
if (arIntegers[i] <= pivotValue)
{
swap(arIntegers[i], arIntegers[storeIndex]);
storeIndex++;
}
}
swap(arIntegers[storeIndex], arIntegers[right]);
return storeIndex;
}
// Simple swap function for our in place swapping.
void swap(int &val1, int &val2)
{
int temp = val1;
val1 = val2;
val2 = temp;
}
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