// To implement merge sort

#include <stdio.h>
#include <stdlib.h>
#define MAX 20

void display(int a[], int n){
    int i;
    printf("\n Elements in array: ");
    for( i=0; i<n; i++)
        printf(" %d ", a[i]);
}

void merge(int ary[], int left,int mid, int right){
    int tmpary[MAX];
    int i=left, j=mid+1, k=left;

    // first fill tmpary in sorted manner
    while( (i<=mid) && (j<=right) ){
        if( ary[i] < ary[j])
            tmpary[k++] = ary[i++];
        else
            tmpary[k++] = ary[j++];
    }
    while( i<=mid )
        tmpary[k++] = ary[i++];
    while( j<=right )
        tmpary[k++] = ary[j++];

    // copy tmpary back to ary
    for( i=left; i<=right; i++)
        ary[i] = tmpary[i];
}

void sort(int ary[], int left,int right){
    int mid = (left+right)/2;
    
    if( left>=right)
        return;

    sort( ary, left, mid);
    sort( ary, mid+1, right);
    merge( ary, left, mid, right);
}

int main(){
    int a[20];
    int n, i;
    
    printf("\n Enter total number of elements in array (max. %d): ", MAX);
    scanf("%d", &n);
    
    if( n < 0)
        printf("UNDERFLOW \n");
    else if( n > MAX)
        printf("OVERFLOW \n");
    else{
        // input elements one by one
        printf("\n Enter item(s) one by one\n");
        for( i=0; i<n; i++){
            printf(" Enter item no %d : ",i);
            scanf("%d", &a[i]);
        }
        
        printf("\n Before Sorting");
        display(a,n);
        sort( a, 0, n-1);
        printf("\n After Sorting");
        display(a,n);
        printf("\n ");
    }
        
    system("pause");
    return 0;
}