JavaAlgorithms/Searches/BinarySearch.java

package Searches;

import static java.lang.String.format;

import java.util.Arrays;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;
import java.util.stream.IntStream;

/**
 * Binary search is one of the most popular algorithms The algorithm finds the position of a target
 * value within a sorted array
 *
 * <p>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));
  }
}