# Data Structure: How to implement Merge Sort in C++?

Merging is the process of combining two or more sorted files into a third sorted file. Merge sort is based on the divide and conquer paradigm. It can be explained as …. Let A[p…..r] is given array with indices p = 1 to r = n. Then steps can be
Image Source: http://en.wikipedia.org/wiki/Merge_sort
1. Divide Step: If a given array A has zero or one element, then simply return; it is already sorted. Otherwise split A[p…..r] into two subarrays as A[p….q] and A[q+1…..r] each containing about the half of the elements.
2. Conquer Step: Conquer by recursively sorted the two sub-arrays A[p….q] and A[q+1….r]
3. Combine Step: Combine the elements back in A[p…..r] by merging the two sorted sub-arrays into the sorted sequence. Note that: the recursion bottoms out when the sub-array has just one element. So that it is trivially sorted.

Source Code:

Output:

How many elements? 7
Insert element to sort: 63 78 52 12 99 32 13
The sorted element is
12 13 32 52 63 78 99

Efficiency of merge sort

Since the merge sort cannot have more than logn passes and each pass involving ‘n’ or fewer comparisons, the merge sort requires no more than nlogn comparisons.  Hence the efficiency of merge sort is O(nlogn).
SHARE Data Structure: How to implement Merge Sort in C++?

### 2 Responses

1. bijon guha says:

very helpfull. may your companies touch sky. 🙂

2. maluma says:

hey dude!! your merge sort program does not work for the size of elements =4 .
i think there is something bug or error in it!!