Java/Searches/BinarySearch.java at master · java66liu/Java · GitHub

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package Searches;

import java.util.Arrays;

import java.util.Random;

import java.util.concurrent.ThreadLocalRandom;

import java.util.stream.IntStream;

import static java.lang.String.format;

/**

* Binary search is one of the most popular algorithms

* The algorithm finds the position of a target value within a sorted array

* Worst-case performance O(log n)

* Best-case performance O(1)

* Average performance O(log n)

* Worst-case space complexity O(1)

* @author Varun Upadhyay (https://github.com/varunu28)

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

* @see SearchAlgorithm

* @see IterativeBinarySearch

class BinarySearch implements SearchAlgorithm {

/**

* @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 index of the element

@Override

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

return search(array, key, 0, array.length);

}

/**

* This method implements the Generic Binary Search

* @param array The array to make the binary search

* @param key The number you are looking for

* @param left The lower bound

* @param right The upper bound

* @return the location of the key

**/

private <T extends Comparable<T>> int search(T array[], T key, int left, int right){

if (right < left) return -1; // this means that the key not found

// find median

int median = (left + right) >>> 1;

int comp = key.compareTo(array[median]);

if (comp == 0) {

return median;

} else if (comp < 0) {

return search(array, key, left, median - 1);

} else {

return search(array, key, median + 1, right);

}

// Driver Program

public static void main(String[] args) {

// Just generate data

Random r = ThreadLocalRandom.current();

int size = 100;

int maxElement = 100000;

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

// The element that should be found

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

BinarySearch search = new BinarySearch();

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

System.out.println(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));

}

Java/Searches/BinarySearch.java at master · java66liu/Java · GitHub

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