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- import java.io.IOException;
- import java.io.PrintWriter;
- import java.util.Arrays;
- import java.util.Random;
- /**
- * Generator which creates a test where Java 7 dual-pivot quicksort algorithm runs in O(n^2) time.
- *
- * Number of operations is not the best possible:
- * maximal recursion depth is about n^2 / 5 while best possible result is n^2 / 4.
- *
- * It's because Java 7 checks if array is nearly sorted.
- * If it is, a strange algorithm with something called 'runs' is used.
- * In our case it is not, but in process of this checking Java 7 swaps some elements.
- * I didn't figure out how to maintain these swaps yet. Feel free to improve it!
- *
- * @author Alexey Dergunov
- * @since 1.7
- */
- public class Java7QuicksortKiller implements Runnable {
- private final Random rnd = new Random(239);
- private final int INSERTION_SORT_THRESHOLD = 47;
- // private final int MAX_RUN_LENGTH = 33;
- // private final int QUICKSORT_THRESHOLD = 286;
- // private final int MAX_RUN_COUNT = 67;
- private int MIN_VALUE;
- private int MAX_VALUE;
- private final int NO_VALUE = -1;
- private void hackedSort(int[] a, int[] p, int left, int right, boolean leftmost) {
- int length = right - left + 1;
- // Use insertion sort on tiny arrays
- if (length < INSERTION_SORT_THRESHOLD) {
- for (int i = right; i >= left; i--) {
- if (a[i] == NO_VALUE) a[i] = MIN_VALUE++;
- }
- randomShuffle(a, left, right); // why not?
- if (leftmost) {
- /*
- * Traditional (without sentinel) insertion sort,
- * optimized for server VM, is used in case of
- * the leftmost part.
- */
- for (int i = left, j = i; i < right; j = ++i) {
- int ai = a[i + 1];
- int pi = p[i + 1];
- while (ai < a[j]) {
- a[j + 1] = a[j];
- p[j + 1] = p[j];
- if (j-- == left) {
- break;
- }
- }
- a[j + 1] = ai;
- p[j + 1] = pi;
- }
- } else {
- /*
- * Skip the longest ascending sequence.
- */
- do {
- if (left >= right) {
- return;
- }
- } while (a[++left] >= a[left - 1]);
- /*
- * Every element from adjoining part plays the role
- * of sentinel, therefore this allows us to avoid the
- * left range check on each iteration. Moreover, we use
- * the more optimized algorithm, so called pair insertion
- * sort, which is faster (in the context of Quicksort)
- * than traditional implementation of insertion sort.
- */
- for (int k = left; ++left <= right; k = ++left) {
- int a1 = a[k], a2 = a[left];
- int p1 = p[k], p2 = p[left];
- if (a1 < a2) {
- a2 = a1; a1 = a[left];
- p2 = p1; p1 = p[left];
- }
- while (a1 < a[--k]) {
- a[k + 2] = a[k];
- p[k + 2] = p[k];
- }
- ++k;
- a[k + 1] = a1;
- p[k + 1] = p1;
- while (a2 < a[--k]) {
- a[k + 1] = a[k];
- p[k + 1] = p[k];
- }
- a[k + 1] = a2;
- p[k + 1] = p2;
- }
- int last = a[right];
- int plast = p[right];
- while (last < a[--right]) {
- a[right + 1] = a[right];
- p[right + 1] = p[right];
- }
- a[right + 1] = last;
- p[right + 1] = plast;
- }
- return;
- }
- // Inexpensive approximation of length / 7
- int seventh = (length >> 3) + (length >> 6) + 1;
- /*
- * Sort five evenly spaced elements around (and including) the
- * center element in the range. These elements will be used for
- * pivot selection as described below. The choice for spacing
- * these elements was empirically determined to work well on
- * a wide variety of inputs.
- */
- int e3 = (left + right) >>> 1; // The midpoint
- int e2 = e3 - seventh;
- int e1 = e2 - seventh;
- int e4 = e3 + seventh;
- int e5 = e4 + seventh;
- if (a[e5] == NO_VALUE) a[e5] = MIN_VALUE++;
- if (a[e4] == NO_VALUE) a[e4] = MIN_VALUE++;
- if (a[e1] == NO_VALUE) a[e1] = MAX_VALUE--;
- if (a[e2] == NO_VALUE) a[e2] = MAX_VALUE--;
- // Sort these elements using insertion sort
- if (less(a[e2], a[e1])) { int t = a[e2]; a[e2] = a[e1]; a[e1] = t;
- int s = p[e2]; p[e2] = p[e1]; p[e1] = s; }
- if (less(a[e3], a[e2])) { int t = a[e3]; a[e3] = a[e2]; a[e2] = t;
- int s = p[e3]; p[e3] = p[e2]; p[e2] = s;
- if (less(t, a[e1])) { a[e2] = a[e1]; a[e1] = t;
- p[e2] = p[e1]; p[e1] = s; }
- }
- if (less(a[e4], a[e3])) { int t = a[e4]; a[e4] = a[e3]; a[e3] = t;
- int s = p[e4]; p[e4] = p[e3]; p[e3] = s;
- if (less(t, a[e2])) { a[e3] = a[e2]; a[e2] = t;
- p[e3] = p[e2]; p[e2] = s;
- if (less(t, a[e1])) { a[e2] = a[e1]; a[e1] = t;
- p[e2] = p[e1]; p[e1] = s; }
- }
- }
- if (less(a[e5], a[e4])) { int t = a[e5]; a[e5] = a[e4]; a[e4] = t;
- int s = p[e5]; p[e5] = p[e4]; p[e4] = s;
- if (less(t, a[e3])) { a[e4] = a[e3]; a[e3] = t;
- p[e4] = p[e3]; p[e3] = s;
- if (less(t, a[e2])) { a[e3] = a[e2]; a[e2] = t;
- p[e3] = p[e2]; p[e2] = s;
- if (less(t, a[e1])) { a[e2] = a[e1]; a[e1] = t;
- p[e2] = p[e1]; p[e1] = s; }
- }
- }
- }
- // Pointers
- int less = left; // The index of the first element of center part
- int great = right; // The index before the first element of right part
- if (a[e1] != a[e2] && a[e2] != a[e3] && a[e3] != a[e4] && a[e4] != a[e5]) {
- /*
- * Use the second and fourth of the five sorted elements as pivots.
- * These values are inexpensive approximations of the first and
- * second terciles of the array. Note that pivot1 <= pivot2.
- */
- int pivot1 = a[e2];
- int pivot2 = a[e4];
- int ppivot1 = p[e2];
- int ppivot2 = p[e4];
- /*
- * The first and the last elements to be sorted are moved to the
- * locations formerly occupied by the pivots. When partitioning
- * is complete, the pivots are swapped back into their final
- * positions, and excluded from subsequent sorting.
- */
- a[e2] = a[left];
- a[e4] = a[right];
- p[e2] = p[left];
- p[e4] = p[right];
- /*
- * Skip elements, which are less or greater than pivot values.
- */
- //while (a[++less] < pivot1);
- //while (a[--great] > pivot2);
- while (less(a[++less], pivot1));
- while (greater(a[--great], pivot2));
- /*
- * Partitioning:
- *
- * left part center part right part
- * +--------------------------------------------------------------+
- * | < pivot1 | pivot1 <= && <= pivot2 | ? | > pivot2 |
- * +--------------------------------------------------------------+
- * ^ ^ ^
- * | | |
- * less k great
- *
- * Invariants:
- *
- * all in (left, less) < pivot1
- * pivot1 <= all in [less, k) <= pivot2
- * all in (great, right) > pivot2
- *
- * Pointer k is the first index of ?-part.
- */
- outer:
- for (int k = less - 1; ++k <= great; ) {
- int ak = a[k];
- int pk = p[k];
- //if (ak < pivot1) { // Move a[k] to left part
- if (less(ak, pivot1)) { // Move a[k] to left part
- a[k] = a[less];
- p[k] = p[less];
- /*
- * Here and below we use "a[i] = b; i++;" instead
- * of "a[i++] = b;" due to performance issue.
- */
- a[less] = ak;
- p[less] = pk;
- ++less;
- //} else if (ak > pivot2) { // Move a[k] to right part
- } else if (greater(ak, pivot2)) { // Move a[k] to right part
- //while (a[great] > pivot2) {
- while (greater(a[great], pivot2)) {
- if (great-- == k) {
- break outer;
- }
- }
- //if (a[great] < pivot1) { // a[great] <= pivot2
- if (less(a[great], pivot1)) { // a[great] <= pivot2
- a[k] = a[less];
- p[k] = p[less];
- a[less] = a[great];
- p[less] = p[great];
- ++less;
- } else { // pivot1 <= a[great] <= pivot2
- a[k] = a[great];
- p[k] = p[great];
- }
- /*
- * Here and below we use "a[i] = b; i--;" instead
- * of "a[i--] = b;" due to performance issue.
- */
- a[great] = ak;
- p[great] = pk;
- --great;
- }
- }
- // Swap pivots into their final positions
- a[left] = a[less - 1]; a[less - 1] = pivot1;
- a[right] = a[great + 1]; a[great + 1] = pivot2;
- p[left] = p[less - 1]; p[less - 1] = ppivot1;
- p[right] = p[great + 1]; p[great + 1] = ppivot2;
- // Sort left and right parts recursively, excluding known pivots
- hackedSort(a, p, left, less - 2, leftmost);
- hackedSort(a, p, great + 2, right, false);
- /*
- * If center part is too large (comprises > 4/7 of the array),
- * swap internal pivot values to ends.
- */
- if (less < e1 && e5 < great) {
- /*
- * Skip elements, which are equal to pivot values.
- */
- while (a[less] == pivot1) {
- throw new RuntimeException("We should not enter here!");
- // ++less;
- }
- while (a[great] == pivot2) {
- throw new RuntimeException("We should not enter here!");
- // --great;
- }
- /*
- * Partitioning:
- *
- * left part center part right part
- * +----------------------------------------------------------+
- * | == pivot1 | pivot1 < && < pivot2 | ? | == pivot2 |
- * +----------------------------------------------------------+
- * ^ ^ ^
- * | | |
- * less k great
- *
- * Invariants:
- *
- * all in (*, less) == pivot1
- * pivot1 < all in [less, k) < pivot2
- * all in (great, *) == pivot2
- *
- * Pointer k is the first index of ?-part.
- */
- outer:
- for (int k = less - 1; ++k <= great; ) {
- int ak = a[k];
- int pk = p[k];
- if (ak == pivot1) { // Move a[k] to left part
- a[k] = a[less];
- p[k] = p[less];
- a[less] = ak;
- p[less] = pk;
- ++less;
- } else if (ak == pivot2) { // Move a[k] to right part
- while (a[great] == pivot2) {
- if (great-- == k) {
- break outer;
- }
- }
- if (a[great] == pivot1) { // a[great] < pivot2
- a[k] = a[less];
- p[k] = p[less];
- /*
- * Even though a[great] equals to pivot1, the
- * assignment a[less] = pivot1 may be incorrect,
- * if a[great] and pivot1 are floating-point zeros
- * of different signs. Therefore in float and
- * double sorting methods we have to use more
- * accurate assignment a[less] = a[great].
- */
- a[less] = pivot1;
- p[less] = ppivot1;
- ++less;
- } else { // pivot1 < a[great] < pivot2
- a[k] = a[great];
- p[k] = p[great];
- }
- a[great] = ak;
- p[great] = pk;
- --great;
- }
- }
- }
- // Sort center part recursively
- hackedSort(a, p, less, great, false);
- } else { // Partitioning with one pivot
- throw new RuntimeException("We should not enter here!");
- // /*
- // * Use the third of the five sorted elements as pivot.
- // * This value is inexpensive approximation of the median.
- // */
- // int pivot = a[e3];
- // int ppivot = p[e3];
- //
- // /*
- // * Partitioning degenerates to the traditional 3-way
- // * (or "Dutch National Flag") schema:
- // *
- // * left part center part right part
- // * +-------------------------------------------------+
- // * | < pivot | == pivot | ? | > pivot |
- // * +-------------------------------------------------+
- // * ^ ^ ^
- // * | | |
- // * less k great
- // *
- // * Invariants:
- // *
- // * all in (left, less) < pivot
- // * all in [less, k) == pivot
- // * all in (great, right) > pivot
- // *
- // * Pointer k is the first index of ?-part.
- // */
- // for (int k = less; k <= great; ++k) {
- // if (a[k] == pivot) {
- // continue;
- // }
- // int ak = a[k];
- // int pk = p[k];
- // if (less(ak, pivot)) { // Move a[k] to left part
- // a[k] = a[less];
- // p[k] = p[less];
- // a[less] = ak;
- // p[less] = pk;
- // ++less;
- // } else { // a[k] > pivot - Move a[k] to right part
- // while (greater(a[great], pivot)) {
- // --great;
- // }
- // if (less(a[great], pivot)) { // a[great] <= pivot
- // a[k] = a[less];
- // p[k] = p[less];
- // a[less] = a[great];
- // p[less] = p[great];
- // ++less;
- // } else { // a[great] == pivot
- // /*
- // * Even though a[great] equals to pivot, the
- // * assignment a[k] = pivot may be incorrect,
- // * if a[great] and pivot are floating-point
- // * zeros of different signs. Therefore in float
- // * and double sorting methods we have to use
- // * more accurate assignment a[k] = a[great].
- // */
- // a[k] = pivot;
- // p[k] = ppivot;
- // }
- // a[great] = ak;
- // p[great] = pk;
- // --great;
- // }
- // }
- //
- // /*
- // * Sort left and right parts recursively.
- // * All elements from center part are equal
- // * and, therefore, already sorted.
- // */
- // hackedSort(a, p, left, less - 1, leftmost, depth + 1);
- // hackedSort(a, p, great + 1, right, false, depth + 1);
- }
- }
- private void randomShuffle(int[] a, int left, int right) {
- for (int i = left; i <= right; i++) {
- int j = left + rnd.nextInt(i - left + 1);
- swap(a, i, j);
- }
- }
- private void swap(int[] a, int i, int j) {
- int t = a[i];
- a[i] = a[j];
- a[j] = t;
- }
- private boolean less(int a, int b) {
- if (a != NO_VALUE && b != NO_VALUE) {
- return a < b;
- }
- if (a == NO_VALUE) {
- return b > MAX_VALUE;
- }
- if (b == NO_VALUE) {
- return a < MIN_VALUE;
- }
- throw new RuntimeException("We should not enter here!");
- }
- private boolean greater(int a, int b) {
- if (a != NO_VALUE && b != NO_VALUE) {
- return a > b;
- }
- if (a == NO_VALUE) {
- return b < MIN_VALUE;
- }
- if (b == NO_VALUE) {
- return a > MAX_VALUE;
- }
- throw new RuntimeException("We should not enter here!");
- }
- public void run() {
- int n = 60000;
- int[] a = new int[n];
- int[] p = new int[n];
- for (int i = 0; i < n; i++) {
- a[i] = NO_VALUE;
- p[i] = i;
- }
- MIN_VALUE = 1;
- MAX_VALUE = n;
- long t1, t2;
- t1 = System.currentTimeMillis();
- hackedSort(a, p, 0, n-1, true);
- t2 = System.currentTimeMillis();
- System.out.println("Generation time = " + (t2 - t1) + " ms.");
- checkValues(a, 1, n);
- checkValues(p, 0, n-1);
- applyPermutation(a, p);
- /*
- try {
- printArray(a, new PrintWriter("output.txt"));
- } catch (IOException e) {
- throw new RuntimeException(e);
- }
- */
- t1 = System.currentTimeMillis();
- Arrays.sort(a.clone());
- t2 = System.currentTimeMillis();
- System.out.println("Sorting time = " + (t2 - t1) + " ms.");
- }
- private void applyPermutation(int[] a, int[] pos) {
- int n = a.length;
- int[] tmp = new int[n];
- for (int i = 0; i < n; i++) {
- tmp[pos[i]] = a[i];
- }
- for (int i = 0; i < n; i++) {
- a[i] = tmp[i];
- pos[i] = i;
- }
- }
- private void checkValues(int[] a, int min, int max) {
- boolean[] b = new boolean[max - min + 1];
- for (int x : a) {
- if (b[x - min]) {
- throw new RuntimeException();
- }
- b[x - min] = true;
- }
- }
- private void printArray(int[] a, PrintWriter pw) {
- int n = a.length;
- pw.println(n);
- for (int i = 0; i < n; i++) {
- pw.print(a[i]);
- if (i == n-1) pw.println(); else pw.print(' ');
- }
- pw.close();
- }
- public static void main(String[] args) {
- new Thread(null, new Java7QuicksortKiller(), "", 128*1024*1024).start();
- }
- }
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