wf.utils.java.algoritms.searches.BinarySearch Maven / Gradle / Ivy
package wf.utils.java.algoritms.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
*/
public 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 is any comparable type
* @return index of the element
*/
@Override
public > int find(T[] array, T key) {
return search(array, key, 0, array.length - 1);
}
/**
* 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 > 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
)
);
}
}