JavaAlgorithms/Searches/IterativeBinarySearch.java

package Searches;

import static java.lang.String.format;

import java.util.Arrays;
import java.util.Random;
import java.util.stream.Stream;

/**
 * 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) >>> 1;
      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));
  }
}