Java/src/main/java/com/thealgorithms/searches/IterativeTernarySearch.java

package com.thealgorithms.searches;

import static java.lang.String.format;

import com.thealgorithms.devutils.searches.SearchAlgorithm;
import java.util.Arrays;
import java.util.Random;
import java.util.stream.Stream;

/**
 * A iterative version of a ternary search algorithm This is better way to
 * implement the ternary search, because a recursive version adds some overhead
 * to a stack. But in java the compile can transform the recursive version to
 * iterative implicitly, so there are no much differences between these two
 * algorithms
 *
 * <p>
 * Worst-case performance Θ(log3(N)) Best-case performance O(1) Average
 * performance Θ(log3(N)) Worst-case space complexity O(1)
 *
 * @author Podshivalov Nikita (https://github.com/nikitap492)
 * @see SearchAlgorithm
 * @see TernarySearch
 * @since 2018-04-13
 */
public class IterativeTernarySearch implements SearchAlgorithm {

    @Override
    public <T extends Comparable<T>> int find(T[] array, T key) {
        int left = 0;
        int right = array.length - 1;

        while (right > left) {
            int leftCmp = array[left].compareTo(key);
            int rightCmp = array[right].compareTo(key);
            if (leftCmp == 0) {
                return left;
            }
            if (rightCmp == 0) {
                return right;
            }

            int leftThird = left + (right - left) / 3 + 1;
            int rightThird = right - (right - left) / 3 - 1;

            if (array[leftThird].compareTo(key) <= 0) {
                left = leftThird;
            } else {
                right = rightThird;
            }
        }

        return -1;
    }

    public static void main(String[] args) {
        // just generate data
        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)];

        IterativeTernarySearch search = new IterativeTernarySearch();
        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
            )
        );
    }
}