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package Searches;

import java.util.Arrays;

import java.util.Random;

import java.util.stream.Stream;

import static java.lang.String.format;

/**

* 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));

}

}