Sorting Algorithms

Files
file	merge_sort.cpp
	Merege Sort Algorithm (MEREGE SORT) implementation

Functions
void	merge (int *arr, int l, int m, int r)
void	mergeSort (int *arr, int l, int r)
void	show (int *arr, int size)
int	main ()

Detailed Description

Function Documentation

main()

int main

(

)

Main function

           {
    int size;
    std::cout << "Enter the number of elements : ";
    std::cin >> size;
    int *arr = new int[size];
    std::cout << "Enter the unsorted elements : ";
    for (int i = 0; i < size; ++i) {
        std::cin >> arr[i];
    }
    mergeSort(arr, 0, size - 1);
    std::cout << "Sorted array : ";
    show(arr, size - 1);
    delete[] arr;
    return 0;
}

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merge()

void merge	(	int *	arr,
		int	l,
		int	m,
		int	r
	)

The merge() function is used for merging two halves. The merge(arr, l, m, r) is key process that assumes that arr[l..m] and arr[m+1..r] are sorted and merges the two sorted sub-arrays into one.

Parameters

arr	- array with two halves arr[l...m] and arr[m+1...l]
l	- left index or start index of first half array
m	- right index or end index of first half array

(The second array starts form m+1 and goes till l)

Parameters

l	- end index or right index of second half array

                                          {
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;
 
    int *L = new int[n1], *R = new int[n2];
 
    for (i = 0; i < n1; i++) L[i] = arr[l + i];
    for (j = 0; j < n2; j++) R[j] = arr[m + 1 + j];
 
    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        } else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }
 
    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }
 
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
 
    delete[] L;
    delete[] R;
}

mergeSort()

void mergeSort	(	int *	arr,
		int	l,
		int	r
	)

Merge sort is a divide and conquer algorithm, it divides the input array into two halves and calls itself for the two halves and then calls merge() to merge the two halves

Parameters

arr	- array to be sorted
l	- left index or start index of array
r	- right index or end index of array

                                       {
    if (l < r) {
        int m = l + (r - l) / 2;
        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);
        merge(arr, l, m, r);
    }
}

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show()

void show	(	int *	arr,
		int	size
	)

Utility function used to print the array after sorting

                              {
    for (int i = 0; i < size; i++) std::cout << arr[i] << " ";
    std::cout << "\n";
}