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;
}

// this code is contributed by shivanisinghss2110