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package com.search;

import java.util.Arrays;

/**

* Exponential search (also called doubling search or galloping search or Struzik search) is an algorithm which finds

* the position of a target value within an array. It works by determining a range that the search key resides in and

* performing a binary search within that range

* <p>

* Worst-case performance O(n)

* Best-case performance O(1)

* Average performance O(Log n)

* Worst-case space complexity O(Log n)

*/

public class ExponentialSearch {

/**

* @param array is an array where the element should be found

* @param key is an element which should be found

* @param <T> is any comparable type

* @return The index position of the key in the array, returns -1 for empty array

*/

public <T extends Comparable<T>> int findIndex(T[] array, T key) {

if (array == null || array.length == 0) {

return -1;

}

int size = array.length;

// If the element is present at first position

if (array[0] == key)

return 0;

// Find the range for binary search by repeated doubling

int i = 1;

while (i < size && array[i].compareTo(key) <= 0) {

i <<= 1;

}

// Call binary search for the range found

return Arrays.binarySearch(array, i >> 1, Math.min(i, size), key);

}

}