# Merge Sort in Data Structure

Level : Advanced
Mentor: Shailendra Chauhan
Duration : 00:03:00

## What is the Merge Sort Algorithm in Data Structures?

An algorithm for sorting that uses the divide-and-conquer strategy is called merge sort. It works by recursively breaking the input array into smaller subarrays, sorting those subarrays, and then merging them back together to form the sorted array.

## Divide and Conquer Method

Merge Sort refers to the Divide and Conquer method. This strategy divides an issue into subproblems. The solution is found by solving each sub-problem individually. Finally, the results of the subproblems are integrated to create the final answer.

## Working of Merge Sort

Merge sort is a common sorting algorithm identified for its speed and stability. To sort a given array of elements, it uses the divide-and-conquer algorithm.

• Divide: Recursively split the array in half.
• Conquer: Sort each part with merge sort.
• Merge: Combine sorted halves to create a single sorted array.

## Complexity Analysis of Merge Sort Algorithm

### Time Complexity

#### Best Case Complexity

This occurs when no sorting is necessary, implying that the array is already sorted. The best-case time complexity for merging sort is O(n*logn).

#### Average Case Complexity

This arises when the array elements are jumbled and do not appropriately climb or descend. The average case time complexity for merge sort is O(n*logn).

#### Worst Case Complexity

This occurs when array members must be sorted in reverse order. That is, assume you need to sort the array elements in ascending order but the elements are in descending order. The worst-case time complexity of merge sort is O(n * logn).

### Space Complexity

We need an additional sorted array to store the final sorted array, hence the space-time complexity is O(n).

## Applications of Merge Sort Algorithm

• Sorting: Easily sort big arrays of numbers or strings.
• External Sorting: Handles big datasets by breaking them down into manageable bits before sorting.
• Database Operations: Used to sort data and optimize queries in databases.
• Parallel Processing: Divided into sub-tasks for parallel execution, which increases efficiency.
• Computer Graphics: Depth sorting is used to determine object rendering order in 3D graphics.

## Advantages of Merge Sort Algorithm

• Stable Sorting: Maintains the order of equal elements, making it appropriate for arrays that contain several fields.
• Good performance: O(nlogn) time complexity, ideal for huge datasets and parallel processing.
• No Worst-Case: Unlike quicksort, there is never an O(nlogn) worst-case.
• Easy Implementation: The divide-and-conquer strategy makes implementation simple.
• Memory Efficiency: In-place sorting requires no extra memory.

## Disadvantages of Merge Sort Algorithm

• Space Complexity: Sub-arrays require O(n) more memory, making them difficult to use with limited memory or large amounts of data.
• Not In-place: Requires additional memory, which is problematic for memory-constrained or huge datasets.
• Complexity: O(n log n) time complexity is not always efficient for small datasets; simpler methods may be preferable.
• Recursive: With big inputs, the recursive nature raises the risk of stack overflow.
• Not Adaptive: Performance varies little depending on the initial data order, making it unsuitable for partially sorted data.
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