Flatland Space Stations Hacker Rank Solution in C- using merge sort

 https://www.hackerrank.com/challenges/flatland-space-stations/problem

#include <stdio.h>

#define MAX 10000

int c[MAX];

void merge(int a[], int ,int ,int , int );

void mergesort(int a[], int ,int);

void mergesort(int a[],int low, int high)

{

                int mid;

                if(low<high)

                {

                                mid=(low+high)/2;

                                mergesort(a,low,mid);

                                mergesort(a, mid+1,high);

                                merge(a,low,mid,mid+1,high);

                }

}

/* merge two subparts obtained by dividing the array into 2 halves (low1 to high1 and low2 to high2)*/

void merge(int a[], int low1,int high1,int low2, int high2)

{

                int i,j,k;

                i=low1;

                j=low2;

                k=low1;    /*after merging, lower index of merged array begins with low1,ends with high2*/

                while(i<= high1 && j<=high2)

                {

                                while(a[i]<=a[j] && i <=high1)

                                {

                                                c[k++]=a[i++];

                                }

                                while(a[j]<a[i]&& j <= high2)

                                {

                                                c[k++]=a[j++];

                                }

                }

                while(i<=high1)    /* if i <= high1 means there are elements still in subpart1 (low1 to high1)*/

                {

                                c[k++]=a[i++];  

                }

                while(j<=high2)

                {

                                c[k++]=a[j++];                  

                }

                for(k=low1;k<=high2;k++)  /* the sorted sub array in 'c' is written back to original array 'a'*/

                {

                                a[k]=c[k];

                }             

}

int main()

{

    int n,m;

    scanf("%d%d",&n,&m);

    int a[m];

    for(int i=0;i<m;i++)

        scanf("%d",&a[i]);

    mergesort(a,0,m-1);

    int max=a[0];

    for(int i=1;i<m;i++)

    {

        if(max<(a[i]-a[i-1])/2)

            max=(a[i]-a[i-1])/2;

    }

    if(n-1-a[m-1] > max)

        max=n-1-a[m-1];

    printf("%d",max);

}