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Old 04-15-2008, 09:40 PM
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Quick sort with median-of-three partitioning
Code:
public class AnotherQuickSort { private long[] data; private int len; public AnotherQuickSort(int max) { data = new long[max]; len = 0; } public void insert(long value) { data[len] = value; // insert and increment size len++; } public void display() { System.out.print("Data:"); for (int j = 0; j < len; j++) System.out.print(data[j] + " "); System.out.println(""); } public void quickSort() { recQuickSort(0, len - 1); } public void recQuickSort(int left, int right) { int size = right - left + 1; if (size <= 3) // manual sort if small manualSort(left, right); else // quicksort if large { long median = medianOf3(left, right); int partition = partitionIt(left, right, median); recQuickSort(left, partition - 1); recQuickSort(partition + 1, right); } } public long medianOf3(int left, int right) { int center = (left + right) / 2; // order left & center if (data[left] > data[center]) swap(left, center); // order left & right if (data[left] > data[right]) swap(left, right); // order center & right if (data[center] > data[right]) swap(center, right); swap(center, right - 1); // put pivot on right return data[right - 1]; // return median value } public void swap(int dex1, int dex2) { long temp = data[dex1]; data[dex1] = data[dex2]; data[dex2] = temp; } public int partitionIt(int left, int right, long pivot) { int leftPtr = left; // right of first elem int rightPtr = right - 1; // left of pivot while (true) { // find bigger while (data[++leftPtr] < pivot) ; // find smaller while (data[--rightPtr] > pivot) ; if (leftPtr >= rightPtr) // if pointers cross, partition done break; else // not crossed, so swap(leftPtr, rightPtr); // swap elements } swap(leftPtr, right - 1); // restore pivot return leftPtr; // return pivot location } public void manualSort(int left, int right) { int size = right - left + 1; if (size <= 1) return; // no sort necessary if (size == 2) { // 2-sort left and right if (data[left] > data[right]) swap(left, right); return; } else // size is 3 { // 3-sort left, center, & right if (data[left] > data[right - 1]) swap(left, right - 1); // left, center if (data[left] > data[right]) swap(left, right); // left, right if (data[right - 1] > data[right]) swap(right - 1, right); // center, right } } public static void main(String[] args) { int maxSize = 16; AnotherQuickSort arr = new AnotherQuickSort(maxSize); for (int j = 0; j < maxSize; j++) { // random numbers long n = (int) (java.lang.Math.random() * 99); arr.insert(n); } arr.display(); arr.quickSort(); arr.display(); } }
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