create quicksort.c

Author: pfatima

Diff for: labPrograms/quicksort.c

@@ -0,0 +1,72 @@
+// Lab Program 1
+// Quicksort (divide & conquer)
+// Avg/Best Time Complexity: O(n*log(n))
+// Worst Time Complexity: O(n^2)
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+void swap(int *a, int *b)
+{
+    int temp = *a;
+    *a = *b;
+    *b = temp;
+}
+
+void display(int arr[], int n)
+{
+    int i;
+    for(i = 0; i < n; i++)
+        printf("%d\t", arr[i]);
+}
+
+int partition(int arr[], int low, int high)
+{
+    int i = low - 1, j = high, pivot = arr[low];
+    while(i < j)
+    {
+        while(i < high && arr[i] <= pivot)
+            i++;
+        while(j > low && arr[j] >= pivot)
+            j--;
+        if(i < j)
+            swap(&arr[i], &arr[j]);
+    }
+    swap(&arr[low], &arr[j]);
+    return j;
+}
+
+void quicksort(int arr[], int low, int high)
+{
+    if (low < high)
+    {
+        int pivotindex = partition(arr, low, high);
+        quicksort(arr, low, pivotindex - 1);
+        quicksort(arr, pivotindex + 1, high);
+    }
+}
+
+void main(){
+    int i, n, arr[500];
+    clock_t start = 0, end = 0;
+
+    srand(time(NULL));
+    
+    printf("enter no. of elements:\n");
+    scanf("%d", &n);
+    for(i = 0; i < n; i++)
+        arr[i] = rand() % 500 + 1;
+    
+    printf("random generated array elements:\n");
+    display(arr, n);
+
+    start = clock();
+    quicksort(arr, 0, n-1);
+    end = clock();
+    
+    printf("\nthe sorted elements are:\n");
+    display(arr, n);
+    
+    printf("\ntime taken : %f",(end-start)/(double)CLOCKS_PER_SEC);
+}