Question

Write a C++ program that implements both the recursive binary and mergesort algorithms as described in zyBooks sections 9.4 and 9.5. Prompt the user for the location of a sequence of numbers, via an external file or data entry by the user. If you choose data entry, prompt the user for the number of values and read them into a data structure of your choice. Then use the mergesort algorithm to sort them in ascending order. Finally, prompt for a value for which to use the binary search and return the location if found or indicate it was not found.

Answer 1

#include <iostream>
using namespace std;
void merge(int *,int, int , int );
void merge_sort(int *arr, int low, int high)
{
    int mid;
    if (low < high){
        //divide the array at middle position
        mid=(low+high)/2;
        merge_sort(arr,low,mid);// recursive call
        merge_sort(arr,mid+1,high);//recursive call
        //merge sorted arrays
        merge(arr,low,high,mid);
    }
}
// Merge sort 
void merge(int *arr, int low, int high, int mid)
{
    int i, j, k, c[50];
    i = low;// set i to low ie, start index
    k = low; // set k to low
    j = mid + 1; 
    //place values from arr to c in sorted order.
    while (i <= mid && j <= high) {
        if (arr[i] < arr[j]) {
            c[k] = arr[i];
            k++;
            i++;
        }
        else  {
            c[k] = arr[j];
            k++;
            j++;
        }
    }
    //if any elements are left after previous while loop, place that into c.
    while (i <= mid) {
        c[k] = arr[i];
        k++;
        i++;
    }
    while (j <= high) {
        c[k] = arr[j];
        k++;
        j++;
    }
    //copy c into arr
    for (i = low; i < k; i++)  {
        arr[i] = c[i];
    }
}
//binary search
int binarySearch(int *arr, int l, int r, int x) 
{ 
    if (r >= l) { 
        int mid =  (r + l) / 2; 
  
        // If  element is present at the middle 
        
        if (arr[mid] == x) 
            return mid; 
  
        
        if (arr[mid] > x) {
            return binarySearch(arr, l, mid - 1, x); }//recursive call
        else{
        
        return binarySearch(arr, mid + 1, r, x); }//recursive call
    } 
  
    // We reach here when element is not 
    // present in array 
    return -1; 
} 
 
// read input array and call mergesort
int main()
{
    int myarray[30], num;
    cout<<"Enter number of elements to be sorted:";
    cin>>num;
    cout<<"Enter "<<num<<" elements to be sorted:";
    for (int i = 0; i < num; i++) { cin>>myarray[i];
    }
    merge_sort(myarray, 0, num-1);
    cout<<"Sorted array\n";
    for (int i = 0; i < num; i++)
    {
        cout<<myarray[i]<<"\t";}
     int x;
 cout<<"\nEnter the number to be found:";
 cin>>x;
 int size = sizeof(myarray) / sizeof(myarray[0]);
int result = binarySearch(myarray, 0, size - 1, x);
if(result==-1){
 cout << "Element is not found in array"; }
else{
cout << "Element is found at index " << result;//index position starts from 0.
 }
    
}

Screenshots. Please note that the index position starts at 0.