MERGE SORTING ALGORITHM IN DATA STRUCTURE... ....

MERGE SORT ALGORITHM IN DATA STRUCTURE:>>
                                                                                                      BY SHEELAJ BABU
                                                                                                       B.TECH  - (IIIT-BGP)

(1) -Merge sort is one of the most efficient sorting algorithms.
(2) - It works on the principle of Divide and Conquer.

A merge sort works as follows:

Top-down Merge Sort Implementation:

The top-down merge sort approach is the methodology which uses recursion mechanism. It starts at the Top and proceeds downwards, with each recursive turn asking the same question such as “What is required to be done to sort the array?” and having the answer as, “split the array into two, make a recursive call, and merge the results.”, until one gets to the bottom of the array-tree.

Example: Let us consider an example to understand the approach better.

1. Divide the unsorted list into n sublists, each comprising 1 element (a list of 1 element is supposed sorted).

Top-down Implementation

2. Repeatedly merge sublists to produce newly sorted sublists until there is only 1 sublist remaining. This will be the sorted list.

Merging of two lists done as follows:

The first element of both lists is compared. If sorting in ascending order, the smaller element among two becomes a new element of the sorted list. This procedure is repeated until both the smaller sublists are empty and the newly combined sublist covers all the elements of both the sublists.

Merging of two lists

  

PROGAM FOR MERGE SORT:>

void merge(int *Arr, int start, int mid, int end) {
 // create a temp array
 int temp[end - start + 1];

 // crawlers for both intervals and for temp
 int i = start, j = mid+1, k = 0;

 // traverse both arrays and in each iteration add smaller of both elements in temp 
 while(i <= mid && j <= end) {
  if(Arr[i] <= Arr[j]) {
   temp[k] = Arr[i];
   k += 1; i += 1;
  }
  else {
   temp[k] = Arr[j];
   k += 1; j += 1;
  }
 }

 // add elements left in the first interval 
 while(i <= mid) {
  temp[k] = Arr[i];
  k += 1; i += 1;
 }

 // add elements left in the second interval 
 while(j <= end) {
  temp[k] = Arr[j];
  k += 1; j += 1;
 }

 // copy temp to original interval
 for(i = start; i <= end; i += 1) {
  Arr[i] = temp[i - start]
 }
}

// Arr is an array of integer type
// start and end are the starting and ending index of current interval of Arr

void mergeSort(int *Arr, int start, int end) {

 if(start < end) {
  int mid = (start + end) / 2;
  mergeSort(Arr, start, mid);
  mergeSort(Arr, mid+1, end);
  merge(Arr, start, mid, end);
 }
}

SO, THIS IS BEST PROGRAM FOR MERGE SORTING....