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