Exponential_Search.cpp

// C++ program to find an element x in a
// sorted array using Exponential search.
#include <bits/stdc++.h>
using namespace std;
  
int binarySearch(int arr[], int, int, int);
  
// Returns position of first occurrence of
// x in array
int exponentialSearch(int arr[], int n, int x)
{
    // If x is present at first location itself
    if (arr[0] == x)
        return 0;
  
    // Find range for binary search by
    // repeated doubling
    int i = 1;
    while (i < n && arr[i] <= x)
        i = i*2;
  
    //  Call binary search for the found range.
    return binarySearch(arr, i/2, 
                            min(i, n-1), x);
}
  
// A recursive binary search function. It returns
// location of x in  given array arr[l..r] is
// present, otherwise -1
int binarySearch(int arr[], int l, int r, int x)
{
    if (r >= l)
    {
        int mid = l + (r - l)/2;
  
        // If the element is present at the middle
        // itself
        if (arr[mid] == x)
            return mid;
  
        // If element is smaller than mid, then it
        // can only be present n left subarray
        if (arr[mid] > x)
            return binarySearch(arr, l, mid-1, x);
  
        // Else the element can only be present
        // in right subarray
        return binarySearch(arr, mid+1, r, x);
    }
  
    // We reach here when element is not present
    // in array
    return -1;
}
  
// Driver code
int main(void)
{
   int arr[] = {2, 3, 4, 10, 40};
   int n = sizeof(arr)/ sizeof(arr[0]);
   int x = 10;
   int result = exponentialSearch(arr, n, x);
   (result == -1)? cout <<"Element is not present in array"
                 : cout <<"Element is present at index " << result;
   return 0;
}