Data Structures (BCA) 3rd Sem Previous Year Solved Question Paper 2022

The "Quick Sort" algorithm is a popular sorting algorithm that can be applied using a stack-based approach. Quick Sort is typically implemented using recursion, but you can also use a stack to simulate the recursive calls. This approach is often referred to as the "iterative" or "stack-based" Quick Sort.

Here's a high-level explanation of how Quick Sort can be implemented using a stack:

1. Choose a Pivot Element: Select a pivot element from the array. The choice of the pivot can vary, but a common approach is to pick the last element in the array.

2. Partition the Array: Rearrange the elements in the array so that elements smaller than the pivot are on the left, and elements greater than the pivot are on the right. The pivot is now in its correct sorted position.

3. Push Subarrays onto the Stack: Instead of making recursive calls, we use a stack to keep track of subarrays that need to be sorted. Push the indices of the two subarrays (left and right of the pivot) onto the stack.

4. Repeat: Continue popping subarrays from the stack and partitioning them until the stack is empty. This mimics the recursive calls in the traditional Quick Sort algorithm.

5. Sort Smaller Subarrays First: To ensure the stack doesn't become too large, it's a good practice to push the indices of the smaller subarray first. This reduces the stack space required.

6. Continue Partitioning and Sorting: Repeat the process for each subarray until the entire array is sorted.

By using a stack, you avoid the overhead of recursive function calls and the risk of running out of stack space for large arrays. This iterative approach can be more memory-efficient and may also be faster in some cases.

pseudocode representation of the stack-based Quick Sort:

def quickSort(arr, low, high):

stack = [] # Create an empty stack

stack.append((low, high)) # Push initial indices onto the stack

while stack:

low, high = stack.pop() # Pop indices from the stack

if low < high:

pivot_index = partition(arr, low, high) # Partition the array

stack.append((low, pivot_index - 1)) # Push left subarray

stack.append((pivot_index + 1, high)) # Push right subarray

def partition(arr, low, high):

# Choose a pivot and rearrange elements

# so that elements < pivot are on the left, and elements > pivot are on the right

# Return the pivot index

This stack-based approach allows you to sort an array using the Quick Sort algorithm without the limitations of excessive recursion.