Added Quick Sort and Randomized Quick Sort

I've also explained why randomized quick sort is better.

Author: kartikeysingh6

classical_algorithms/c++/quicksort.cpp

@@ -0,0 +1,44 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+int partition(int A[],int s,int e){
+	int pivot=A[e];
+	int pindx=s;
+	for(int i=s;i<=e-1;i++){
+		if(A[i]<=pivot){
+			swap(A[i],A[pindx]);
+			pindx++;
+		}
+	}
+	swap(A[pindx],A[e]);
+	return pindx;
+}
+
+int randompartition(int A[],int s,int e){
+	int pindx = (rand() %(e - s + 1)) + s;
+	swap(A[pindx],A[e]);
+	return partition(A,s,e);
+}
+
+void quickSort(int *A,int s,int e){
+	if(s>=e)
+		return;
+	int pindx=randompartition(A,s,e);
+	quickSort(A,s,pindx-1);
+	quickSort(A,pindx+1,e);
+}
+
+int main(){
+	int A[]={5,2,7,11,-3,4,66,12};
+	int n=sizeof(A)/sizeof(A[0]);
+	//-3,2,4,5,7,11,12,66
+	quickSort(A,0,n-1);
+
+	for(int i=0;i<n;i++)
+		cout<<A[i]<<" ";
+}
+
+/*NOTE: Randomized Partition is always recommended because if by chance extreme element (minimum or maximum)
+is selected then time complexity will be worst aka O(n^2), Randomized partition increases the probability
+such that non extreme element is selected as pivot this will result in time complexity of O(nlogn), which is
+far better than O(n^2).*/