Mergesort

Mergesort with sentinel element as 5000

void merge(int a[],int p,int q,int r)
{
    int n1=q-p+1;
    int n2=r-q;
    int i,j,k;
    int b[n1+1],c[n2+1];
    for(i=1;i<=n1;i++)
        b[i]=a[p+i-1];
    for(j=1;j<=n2;j++)
        c[j]=a[q+j];
    b[n1+1]=5000;
    c[n2+1]=5000;
    i=1;
    j=1;
    for(k=p;k<=r;k++)
    {
        if(b[i]<=c[j])
        {
            a[k]=b[i];
            i++;
        }
        else
        {
            a[k]=c[j];
            j++;
            
        }
    }
    
    
}
void mergesort(int a[],int p,int r)
{ 
int q;
    if(p<r)
    {
        q=(p+r)/2;
        mergesort(a,p,q);
        mergesort(a,q+1,r);
        merge(a,p,q,r);
    }
 //return 0;
}
int main() {
int a[]={7,1,72,8,400,9};
int i;
int size= sizeof(a)/sizeof(a[0]);
mergesort(a,0,size-1);
for(i=0;i<size;i++)
      printf("%d\t",a[i]);
  printf("\n");
    return 0;
    
}







/*// Merge sort in C

#include <stdio.h>

// Merge two subarrays L and M into arr
void merge(int arr[], int p, int q, int r) {

  // Create L ← A[p..q] and M ← A[q+1..r]
  int n1 = q - p + 1;
  int n2 = r - q;

  int L[n1], M[n2];

  for (int i = 0; i < n1; i++)
    L[i] = arr[p + i];
  for (int j = 0; j < n2; j++)
    M[j] = arr[q + 1 + j];

  // Maintain current index of sub-arrays and main array
  int i, j, k;
  i = 0;
  j = 0;
  k = p;

  // Until we reach either end of either L or M, pick larger among
  // elements L and M and place them in the correct position at A[p..r]
  while (i < n1 && j < n2) {
    if (L[i] <= M[j]) {
      arr[k] = L[i];
      i++;
    } else {
      arr[k] = M[j];
      j++;
    }
    k++;
  }

  // When we run out of elements in either L or M,
  // pick up the remaining elements and put in A[p..r]
  while (i < n1) {
    arr[k] = L[i];
    i++;
    k++;
  }

  while (j < n2) {
    arr[k] = M[j];
    j++;
    k++;
  }
}

// Divide the array into two subarrays, sort them and merge them
void mergeSort(int arr[], int l, int r) {
  if (l < r) {

    // m is the point where the array is divided into two subarrays
    int m = l + (r - l) / 2;

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

    // Merge the sorted subarrays
    merge(arr, l, m, r);
  }
}

// Print the array
void printArray(int arr[], int size) {
  for (int i = 0; i < size; i++)
    printf("%d ", arr[i]);
  printf("\n");
}

// Driver program
int main() {
  int arr[] = {6, 5, 12, 10, 9, 1};
  int size = sizeof(arr) / sizeof(arr[0]);

  mergeSort(arr, 0, size - 1);

  printf("Sorted array: \n");
  printArray(arr, size);
}*/```