Why do we use quicksort instead of heapsort?

Help! Quicksort not working properly!!?

• We were given code for quicksort as part of a larger project and are supposed to modify it to have a random pivot value instead of using the last element, as given in the initial implementation. However, my attempt at randomizing the pivot isn't working (the original worked just fine); when I sort the sequence and output it, it gives me only some of the values in the sequence in order with extra repetitions and leaves some out. What am I doing wrong? template <typename Object, typename Comp> class QuickSort { // QuickSort class protected: Comp comp; void quickSortStep(VectorSequence<Object>& S, int leftBound, int rightBound); // recursive utility public: QuickSort() : comp() {} void sort(VectorSequence<Object>& S); // main entry point }; template <typename Object, typename Comp> void QuickSort<Object, Comp>:: // recursive portion quickSortStep(VectorSequence<Object>& S, int leftBound, int rightBound) { if (leftBound >= rightBound) return; // 0 or 1 elements /***Pivot choice 1: last element. Commented out when not in use*****************/ // Object pivot = S.atRank(rightBound).element(); // select last as pivot /*************************************... /***Pivot choice 2: random element in sequence. Commented out when not used.**************/ srand(time(NULL)); Object pivot = S.atRank(leftBound + rand()%(rightBound-leftBound + 1)).element(); /*************************************... int leftIndex = leftBound; // will scan rightward int rightIndex = rightBound - 1; // will scan leftward while (leftIndex <= rightIndex) { while ((leftIndex <= rightIndex) && // scan right to larger comp(S.atRank(leftIndex).element(), pivot) <= 0) leftIndex++; while ((rightIndex >= leftIndex) && // scan left to smaller comp(S.atRank(rightIndex).element(), pivot) >= 0) rightIndex--; if (leftIndex < rightIndex) // both elements found S.swapElements(S.atRank(leftIndex), S.atRank(rightIndex)); } // until indices cross // Shift right the right half of the sequence // instead of swapping the last element with the middle element int i = rightBound; while (i > leftIndex) { S.replaceAtRank(i, S.atRank(i-1).element()); i--; } // pivot at leftIndex S.replaceAtRank(leftIndex, pivot); // Swap the last element with the middle element //S.swapElements(S.atRank(leftIndex), S.atRank(rightBound)); quickSortStep(S, leftBound, leftIndex-1); // recur on both sides quickSortStep(S, leftIndex+1, rightBound); } template <typename Object, typename Comp> void QuickSort<Object, Comp>:: sort(VectorSequence<Object>& S) { // main entry point if (S.size() <= 1) return; // 0 or 1 elements quickSortStep(S, 0, S.size()-1); // call sort utility }

• Answer:

  Restart the program to make that work... Good luck!