QuickSort - Data Structure and Algorithm Tutorials
QuickSort is a sorting algorithm based on the Divide and Conquer algorithm that picks an element as a pivot and partitions the given array around the picked pivot by placing the pivot in its correct position in the sorted array.
How does QuickSort work?
The key process in QuickSort is a partition(). The target of partitions is to place the pivot (any element can be chosen to be a pivot) at its correct position in the sorted array and put all smaller elements to the left of the pivot, and all greater elements to the right of the pivot.
Partition is done recursively on each side of the pivot after the pivot is placed in its correct position, and this finally sorts the array.
Complexity Analysis of QuickSort
- Time Complexity (Average Case): O(N log N)
- Worst Case Time Complexity: O(N^2)
- Auxiliary Space: O(log N)
Advantages of QuickSort
- Efficient sorting algorithm.
- Well-suited for large datasets.
- More efficient than other O(N^2) sorting algorithms like Bubble Sort or Insertion Sort.
Drawbacks of QuickSort
- Worst-case time complexity is O(N^2).
- Not a stable sorting algorithm.
Applications of QuickSort
QuickSort is widely used in various computer programs, including the C library function qsort, C++ library function sort, and Java library functions Arrays.sort().
Comparison Between QuickSort and Other Sorting Algorithms
| Comparison | QuickSort | Bubble Sort | Insertion Sort |
|---|---|---|---|
| Time Complexity (Average Case) | O(N log N) | O(N^2) | O(N^2) |
| Efficiency | Efficient for large datasets. | Not efficient for large datasets. | Not efficient for large datasets. |
| Stability | Not stable. | Stable. | Stable. |
| Memory Usage | Requires O(log N) auxiliary space. | Requires O(1) auxiliary space. | Requires O(1) auxiliary space. |
Top 20 Interview Questions on Quick Sort
| Question | Difficulty Level |
|---|---|
| What is QuickSort? | Intermediate |
| Explain the concept of Divide and Conquer. | Intermediate |
| What is a pivot element in QuickSort? | Beginner |
| How does QuickSort work? | Intermediate |
| What is the time complexity of QuickSort in the average case? | Intermediate |
| What is the worst-case time complexity of QuickSort? | Intermediate |
| Explain the concept of partitioning in QuickSort. | Intermediate |
| Advantages of QuickSort. | Intermediate |
| Drawbacks of QuickSort. | Intermediate |
| Applications of QuickSort. | Intermediate |
| What is the purpose of using QuickSort? | Beginner |
| What are the conditions for applying QuickSort? | Intermediate |
| What is the time complexity of QuickSort in the worst case? | Intermediate |
| Explain the concept of tail recursion. | Intermediate |
| What is the space complexity of QuickSort? | Intermediate |
| What are the advantages of tail recursion in QuickSort? | Intermediate |
| What are the disadvantages of tail recursion in QuickSort? | Intermediate |
| How is QuickSort different from MergeSort? | Intermediate |
| What are some common mistakes to avoid when implementing QuickSort? | Intermediate |
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