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package Searches;

import java.util.Arrays;

import java.util.Random;

import java.util.stream.Stream;

import static java.lang.String.format;

/**

* Binary search is one of the most popular algorithms

* This class represents iterative version {@link BinarySearch}

* Iterative binary search is likely to have lower constant factors because it doesn't involve the overhead of manipulating the call stack.

* But in java the recursive version can be optimized by the compiler to this version.

* <p>

* Worst-case performance O(log n)

* Best-case performance O(1)

* Average performance O(log n)

* Worst-case space complexity O(1)

*

* @author Gabriele La Greca : https://github.com/thegabriele97

* @author Podshivalov Nikita (https://github.com/nikitap492)

* @see SearchAlgorithm

* @see BinarySearch

*/

public final class IterativeBinarySearch implements SearchAlgorithm {

/**

* This method implements an iterative version of binary search algorithm

*

* @param array a sorted array

* @param key the key to search in array

* @return the index of key in the array or -1 if not found

*/

@Override

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

int l, r, k, cmp;

l = 0;

r = array.length - 1;

while (l <= r) {

k = (l + r) / 2;

cmp = key.compareTo(array[k]);

if (cmp == 0) {

return k;

} else if (cmp < 0) {

r = --k;

} else {

l = ++k;

}

}

return -1;

}

//Only a main method for test purpose

public static void main(String[] args) {

Random r = new Random();

int size = 100;

int maxElement = 100000;

Integer[] integers = Stream.generate(() -> r.nextInt(maxElement)).limit(size).sorted().toArray(Integer[]::new);

//the element that should be found

Integer shouldBeFound = integers[r.nextInt(size - 1)];

IterativeBinarySearch search = new IterativeBinarySearch();

int atIndex = search.find(integers, shouldBeFound);

System.out.println(String.format("Should be found: %d. Found %d at index %d. An array length %d"

, shouldBeFound, integers[atIndex], atIndex, size));

int toCheck = Arrays.binarySearch(integers, shouldBeFound);

System.out.println(format("Found by system method at an index: %d. Is equal: %b", toCheck, toCheck == atIndex));

}

}