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ExponentialSearch.java
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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);
}
}