binary serach for infinite
// Java program to demonstrate working of
// an algorithm that finds an element in an
// array of infinite size
class Test
{
// Simple binary search algorithm
static 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;
}
// Method takes an infinite size array and a key to be
// searched and returns its position if found else -1.
// We don't know size of arr[] and we can assume size to be
// infinite in this function.
// NOTE THAT THIS FUNCTION ASSUMES arr[] TO BE OF INFINITE SIZE
// THEREFORE, THERE IS NO INDEX OUT OF BOUND CHECKING
static int findPos(int arr[],int key)
{
int l = 0, h = 1;
int val = arr[0];
// Find h to do binary search
while (val < key)
{
l = h; // store previous high
//check that 2*h doesn't exceeds array
//length to prevent ArrayOutOfBoundException
if(2*h < arr.length-1)
h = 2*h;
else
h = arr.length-1;
val = arr[h]; // update new val
}
// at this point we have updated low
// and high indices, thus use binary
// search between them
return binarySearch(arr, l, h, key);
}
// Driver method to test the above function
public static void main(String[] args)
{
int arr[] = new int[]{3, 5, 7, 9, 10, 90,
100, 130, 140, 160, 170};
int ans = findPos(arr,10);
if (ans==-1)
System.out.println("Element not found");
else
System.out.println("Element found at index " + ans);
}
}