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