1 C++ 2 void quickSort(int arr[], int left, int right) { 3 int i = left, j = right; 4 int tmp; 5 int pivot = arr[(left + right) / 2]; 6 7 /* partition */ 8 while (i <= j) { 9 while (arr[i] < pivot) 10 i++; 11 while (arr[j] > pivot) 12 j; 13 if (i <= j) { 14 tmp = arr[i]; 15 arr[i] = arr[j]; 16 arr[j] = tmp; 17 i++; 18 j; 19 } 20 }; 21 22 /* recursion */ 23 if (left < j) 24 quickSort(arr, left, j); 25 if (i < right) 26 quickSort(arr, i, right); 27 }
Quicksort is a fast sorting algorithm, which is used not only for educational purposes,but widely applied in practice. On the average, it has O(n log n) complexity, makingquicksort suitable for sorting big data volumes. The idea of the algorithm is quite simpleand once you realize it, you can write quicksort as fast as bubble sort.ForumFeedbackC++ code snippetsEconomics TextbookSupport usto writemore tutorialsAlgorithmThe divide-and-conquer strategy is used in quicksort. Below the recursion step is described:1. Choose a pivot value. We take the value of the middle element as pivot value, but itcan be any value, which is in range of sorted values, even if it doesn't present in thearray.2. Partition. Rearrange elements in such a way, that all elements which are lesser thanthe pivot go to the left part of the array and all elements greater than the pivot, goto the right part of the array. Values equal to the pivot can stay in any part of thearray. Notice, that array may be divided in non-equal parts.3. Sort both parts. Apply quicksort algorithm recursively to the left and the rightparts.Partition algorithm in detailto create newvisualizersto keep sharingfree knowledge for youThere are two indices i and j and at the very beginning of the partition algorithm i pointsto the first element in the array and j points to the last one. Then algorithm moves iforward, until an element with value greater or equal to the pivot is found. Index j ismoved backward, until an element with value lesser or equal to the pivot is found. If i ≤j then they are swapped and i steps to the next position (i + 1), j steps to the previousone (j - 1). Algorithm stops, when i becomes greater than j.After partition, all values before i-th element are less or equal than the pivot and allvalues after j-th element are greater or equal to the pivot.Example. Sort {1, 12, 5, 26, 7, 14, 3, 7, 2} using quicksort.