added quick sort algorithm

Author: caffeine-soul

quicksort.cpp

@@ -0,0 +1,75 @@
+
+/* C implementation QuickSort */
+#include<iostream>
+using namespace std; 
+  
+// A utility function to swap two elements 
+void swap(int* a, int* b) 
+{ 
+    int t = *a; 
+    *a = *b; 
+    *b = t; 
+} 
+  
+/* This function takes last element as pivot, places 
+   the pivot element at its correct position in sorted 
+    array, and places all smaller (smaller than pivot) 
+   to left of pivot and all greater elements to right 
+   of pivot */
+int partition (int arr[], int low, int high) 
+{ 
+    int pivot = arr[high];    // pivot 
+    int i = (low - 1);  // Index of smaller element 
+  
+    for (int j = low; j <= high- 1; j++) 
+    { 
+        // If current element is smaller than or 
+        // equal to pivot 
+        if (arr[j] <= pivot) 
+        { 
+            i++;    // increment index of smaller element 
+            swap(&arr[i], &arr[j]); 
+        } 
+    } 
+    swap(&arr[i + 1], &arr[high]); 
+    return (i + 1); 
+} 
+  
+/* The main function that implements QuickSort 
+ arr[] --> Array to be sorted, 
+  low  --> Starting index, 
+  high  --> Ending index */
+void quickSort(int arr[], int low, int high) 
+{ 
+    if (low < high) 
+    { 
+        /* pi is partitioning index, arr[p] is now 
+           at right place */
+        int pi = partition(arr, low, high); 
+  
+        // Separately sort elements before 
+        // partition and after partition 
+        quickSort(arr, low, pi - 1); 
+        quickSort(arr, pi + 1, high); 
+    } 
+} 
+  
+/* Function to print an array */
+void printArray(int arr[], int size) 
+{ 
+    int i; 
+    for (i=0; i < size; i++) 
+        cout<<arr[i]; 
+  cout<<"\n"; 
+} 
+  
+// Driver program to test above functions 
+int main() 
+{ 
+    int arr[] = {10, 7, 8, 9, 1, 5}; 
+    int n = sizeof(arr)/sizeof(arr[0]); 
+    quickSort(arr, 0, n-1); 
+    cout<< "Sorted array: \n"; 
+    printArray(arr, n); 
+    return 0; 
+}