We often face an interview question when it is asked to search or traverse an array without knowing/using the length property. In Java, if you try to access the element that is outside the length of the array.

it will give you an exception as java.lang.ArrayIndexOutOfBoundsException.

Here I have one implementation of a binary search where I will not use the length property of the array.

### Example

``````import static java.lang.Math.pow;

public class BinarySearchWithoutLength {

public static Integer binarySearch(final Integer[] elements, final Integer find) {
/*
* Start looking for element at the 0th position and move in multiple of 2. like 2^0, 2^1, 2^2,
* 2^3
*/
Integer index = 0;
Integer exp = 0; // initial exponent value will be 0
try {
while (true) {
// check if we found the element at 2^exp index
if (elements[index] == find) {
return index;
}
if (elements[index] < find) {
index = (int) pow(2, exp);
exp += 1;
} else {
break;
}
}
} catch (ArrayIndexOutOfBoundsException e) {
/*
* ignore this exception as we expect it to happen if we go beyond the size of the array
* without finding element at position 2^exp
*/
}
int mid; // it will represent mid value where lookup will happen
int left = (index / 2) + 1;
int right = index - 1;
/*
* we will start our lookup from the middle of the array and then shift towards other half of
* the array.
*/
while (left <= right) {
mid = ((right + left) / 2);
try {
if (elements[mid] == find) {
/*
* As we have found one matching element. Stop
*/
return mid;
} else {
if (elements[mid] > find) {
/* whenever you find and element which is greater than the find */
right = mid - 1;
} else {
left = mid + 1;
}
}
} catch (ArrayIndexOutOfBoundsException e) {
/*
* we got this because we reached beyond the size, shift our right index to one place left
* of the mid
*/
right = mid - 1;
}
}
return -1;
}

public static void main(String[] args) {
Integer[] sample_1 = new Integer[] {-3, -2, 3, 4, 7};
Integer[] sample_2 = new Integer[] {-3, -2, -1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};
Integer[] sample_3 = new Integer[] {1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};
System.out.println("Index of 4: " + binarySearch(sample_1, 4));
System.out.println("Index of 4: " + binarySearch(sample_2, 4));
System.out.println("Index of 4: " + binarySearch(sample_3, 10));
System.out.println("Index of 4: " + binarySearch(sample_3, 0));
}
}
``````