// partitions the array using the first element as pivot
public static int partition(final int a[], final int lo, final int hi) {
int i = lo;
int j = hi + 1;
while (true) {
while (a[++i] < a[lo]) {
if (i == hi) {
break;
}
}
while (a[--j] > a[lo]) {
if (j == lo) {
break;
}
}
if (i >= j) {
break;
}
IntUtils.swap(a, i, j);
}
IntUtils.swap(a, lo, j);
// System.out.println("j="+j);
return j;
}
public static void test_threeWayQuickSort() {
final int a[] = IntUtils.genRandIntArray(10, 12, 10);
// IntUtils.printArray(a);
final long t1 = System.currentTimeMillis();
threeWayQuickSort(a, 0, a.length - 1);
final long t2 = System.currentTimeMillis();
// IntUtils.printArray(a);
System.out.println("3-WAY SORT: Time taken = " + (t2 - t1));
System.out.println("Is resulting array Sorted? " + IntUtils.isSorted(a));
}
public static void test_select() {
final int a[] = IntUtils.genRandIntArray(0, 4, 100);
// IntUtils.printArray(a);
System.out.println("Array generated.");
final int k = 5;
select(a, k);
System.out.println("Select done.");
// IntUtils.printArray(a);
System.out.println(k + "-th largest = " + a[k]);
System.out.println("Largest " + k + " elements:");
IntUtils.printArray(a, k, a.length - 1);
}
public static void threeWayQuickSort(final int a[], final int lo, final int hi) {
if (lo > hi) {
return;
}
final int pivot = a[lo];
int lt = lo;
int gt = hi;
int i = lo;
while (i <= gt) {
if (pivot > a[i]) {
IntUtils.swap(a, i++, lt++);
} else if (pivot < a[i]) {
IntUtils.swap(a, i, gt--);
} else {
i++;
}
}
threeWayQuickSort(a, lo, lt - 1);
threeWayQuickSort(a, gt + 1, hi);
}
public static void test_partition() {
final int a[] = IntUtils.genRandIntArray(10, 99, 10);
IntUtils.printArray(a);
partition(a, 0, a.length - 1);
IntUtils.printArray(a);
}
