Merge pull request #87 from soumya997/soumyadip1

added quick sort using c++

Author: larissalages

classical_algorithms/c++/Quick Sort.cpp

@@ -0,0 +1,68 @@
+// Quick Sort using c++
+#include <iostream>
+using namespace std;
+
+/*
+Here's what is happening, 
+        we are selecting an element as a pivot element, and based on that
+        we are dividing the array by two parts, 1st part is having elements
+        lesser and equal to(<=) the pivot element and 2nd part having elements consists 
+        of larger(>) than the pivot element. After that, we simply sort the two parts 
+        recursively.
+
+        Now, the dividing part is done by the partition function and the sorting 
+        part via the quickSort function.
+
+        average time complexity- NlogN
+        worst time complexity - N^2
+        Approach- Divide and Conquer
+*/
+
+
+
+int partition(int *arr,int s,int e){
+    int i=s-1;
+    int j=s;
+    int pivot=arr[e];
+    for(;j<=e-1;j++){
+        if(arr[j]<=pivot){
+            i=i+1;
+            swap(arr[i],arr[j]);            
+        }
+        
+    }
+    swap(arr[i+1],arr[e]);
+    return i+1;
+}
+
+
+void quickSort(int *arr,int s,int e){
+    // base case
+    if(s>=e){
+        return;
+    }
+    // rec-case
+    int p = partition(arr,s,e);
+    quickSort(arr,s,p-1);
+    quickSort(arr,p+1,e);
+}
+
+
+int main() {
+    int n;
+    cin>>n;
+    int arr[n];
+    
+    for(int i=0;i<n;i++){
+        cin>>arr[i];
+    }
+    // functin call
+    quickSort(arr,0,n-1);
+
+    cout<<"After Quick Sort: ";
+    for(int i=0;i<n;i++){
+        
+        cout<<arr[i]<<" ";
+    }
+}
+