# 13371 - Merge Sorting

## Brief
Please implement a function to execute the merge sort algorithm.

You will be given an integer M which corresponds to the size of the array to be sorted, followed by M number of integers which are the contents of the array.
## Input
Integer M (1 <= M <= 100 000)

M numbr of integers. (all integers will be able to fit in an int variable)
## Output
The contents of the array followed by a newline character.

## Solution 1

//by Keith
#include <stdio.h>
#include <stdlib.h>

void merge(int* arr, int l, int m, int r){
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;
  
    int L[n1], R[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++;
    }
}
  
void mergeSort(int* arr, int l, int r){
    if (l < r) {
        int m = l + (r - l) / 2;

        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);
  
        merge(arr, l, m, r);
    }
}

## Solution 2

//by Keith
int cmp(const void *a, const void *b);

void mergeSort(int a[], int l, int r)
{
	qsort(a, r-l+1, sizeof(int), cmp);	
}

int cmp(const void *a, const void *b)
{
	return *(int *)a - *(int *)b; 
}