Add QuickSort in java (#814)

Author: OttoWBitt

sorting/quick_sort/QuickSort.java

@@ -0,0 +1,61 @@
+class QuickSort {
+	public static void main(String[] args) throws Exception {
+
+		int quantity = 20;
+		int[] vector = new int[quantity];
+
+		for (int i = 0; i < vector.length; i++) {
+			vector[i] = (int) (Math.random() * quantity);
+		}
+
+		System.out.println("Vector before QuickSort: ");
+		for (int i = 0; i < vector.length ; i++ ) {
+			System.out.print(vector[i] + "-");
+		}
+
+		long initialTime = System.currentTimeMillis();
+
+		quickSort(vector, 0, vector.length - 1);
+
+		long finalTime = System.currentTimeMillis();
+
+		System.out.println(" ");
+		System.out.println("Vector after quickSort: ");
+
+		for (int i = 0; i < vector.length ; i++ ) {
+			System.out.print(vector[i] + "-");
+		}
+		System.out.println(" ");
+		System.out.println("Execution time = " + (finalTime - initialTime) + " ms");
+
+	}
+
+	private static void quickSort(int[] vector, int first, int last) {
+		if (first < last) {
+			int referencePosition = separar(vector, first, last);
+			quickSort(vector, first, referencePosition - 1);
+			quickSort(vector, referencePosition + 1, last);
+		}
+	}
+
+	private static int separar(int[] vector, int first, int last) {
+		int reference = vector[first];
+		int i = first + 1, j = last;
+		while (i <= j) {
+			if (vector[i] <= reference)
+				i++;
+			else if (reference < vector[j])
+				j--;
+			else {
+				int swap = vector[i];
+				vector[i] = vector[j];
+				vector[j] = swap;
+				i++;
+				j--;
+			}
+		}
+		vector[first] = vector[j];
+		vector[j] = reference;
+		return j;
+	}
+}