84 lines
2.4 KiB
Java
84 lines
2.4 KiB
Java
package Searches;
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import java.util.Arrays;
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import java.util.Random;
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import java.util.stream.Stream;
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import static java.lang.String.format;
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/**
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* A iterative version of a ternary search algorithm
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* This is better way to implement the ternary search, because a recursive version adds some overhead to a stack.
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* But in java the compile can transform the recursive version to iterative implicitly,
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* so there are no much differences between these two algorithms
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* <p>
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* Worst-case performance Θ(log3(N))
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* Best-case performance O(1)
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* Average performance Θ(log3(N))
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* Worst-case space complexity O(1)
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*
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* @author Podshivalov Nikita (https://github.com/nikitap492)
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* @see SearchAlgorithm
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* @see TernarySearch
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* @since 2018-04-13
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*/
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public class IterativeTernarySearch implements SearchAlgorithm {
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@Override
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public <T extends Comparable<T>> int find(T[] array, T key) {
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int left = 0;
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int right = array.length - 1;
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while (right > left) {
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int leftCmp = array[left].compareTo(key);
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int rightCmp = array[right].compareTo(key);
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if (leftCmp == 0) return left;
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if (rightCmp == 0) return right;
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int leftThird = left + (right - left) / 3 + 1;
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int rightThird = right - (right - left) / 3 - 1;
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if (array[leftThird].compareTo(key) <= 0) {
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left = leftThird;
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} else {
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right = rightThird;
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}
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}
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return -1;
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}
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public static void main(String[] args) {
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//just generate data
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Random r = new Random();
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int size = 100;
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int maxElement = 100000;
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Integer[] integers = Stream.generate(() -> r.nextInt(maxElement))
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.limit(size)
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.sorted()
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.toArray(Integer[]::new);
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//the element that should be found
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Integer shouldBeFound = integers[r.nextInt(size - 1)];
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IterativeTernarySearch search = new IterativeTernarySearch();
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int atIndex = search.find(integers, shouldBeFound);
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System.out.println(format("Should be found: %d. Found %d at index %d. An array length %d",
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shouldBeFound, integers[atIndex], atIndex, size));
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int toCheck = Arrays.binarySearch(integers, shouldBeFound);
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System.out.println(format("Found by system method at an index: %d. Is equal: %b",
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toCheck, toCheck == atIndex));
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}
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}
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