Create threeWayQuickSort.cpp

threeWayQuickSort.cpp

@@ -0,0 +1,102 @@
+// C++ program for 3-way quick sort
+#include <bits/stdc++.h>
+using namespace std;
+
+/* This function partitions a[] in three parts
+a) a[l..i] contains all elements smaller than pivot
+b) a[i+1..j-1] contains all occurrences of pivot
+c) a[j..r] contains all elements greater than pivot */
+void partition(int a[], int l, int r, int& i, int& j)
+{
+	i = l - 1, j = r;
+	int p = l - 1, q = r;
+	int v = a[r];
+
+	while (true) {
+		// From left, find the first element greater than
+		// or equal to v. This loop will definitely
+		// terminate as v is last element
+		while (a[++i] < v)
+			;
+
+		// From right, find the first element smaller than
+		// or equal to v
+		while (v < a[--j])
+			if (j == l)
+				break;
+
+		// If i and j cross, then we are done
+		if (i >= j)
+			break;
+
+		// Swap, so that smaller goes on left greater goes
+		// on right
+		swap(a[i], a[j]);
+
+		// Move all same left occurrence of pivot to
+		// beginning of array and keep count using p
+		if (a[i] == v) {
+			p++;
+			swap(a[p], a[i]);
+		}
+
+		// Move all same right occurrence of pivot to end of
+		// array and keep count using q
+		if (a[j] == v) {
+			q--;
+			swap(a[j], a[q]);
+		}
+	}
+
+	// Move pivot element to its correct index
+	swap(a[i], a[r]);
+
+	// Move all left same occurrences from beginning
+	// to adjacent to arr[i]
+	j = i - 1;
+	for (int k = l; k < p; k++, j--)
+		swap(a[k], a[j]);
+
+	// Move all right same occurrences from end
+	// to adjacent to arr[i]
+	i = i + 1;
+	for (int k = r - 1; k > q; k--, i++)
+		swap(a[i], a[k]);
+}
+
+// 3-way partition based quick sort
+void quicksort(int a[], int l, int r)
+{
+	if (r <= l)
+		return;
+
+	int i, j;
+
+	// Note that i and j are passed as reference
+	partition(a, l, r, i, j);
+
+	// Recur
+	quicksort(a, l, j);
+	quicksort(a, i, r);
+}
+
+// A utility function to print an array
+void printarr(int a[], int n)
+{
+	for (int i = 0; i < n; ++i)
+		printf("%d ", a[i]);
+	printf("\n");
+}
+
+// Driver code
+int main()
+{
+	int a[] = { 4, 9, 4, 4, 1, 9, 4, 4, 9, 4, 4, 1, 4 };
+	int size = sizeof(a) / sizeof(int);
+
+	// Function Call
+	printarr(a, size);
+	quicksort(a, 0, size - 1);
+	printarr(a, size);
+	return 0;
+}