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| 1 | +package search; |
| 2 | + |
| 3 | +import java.util.Arrays; |
| 4 | +import java.util.Random; |
| 5 | +import java.util.stream.Stream; |
| 6 | + |
| 7 | +import static java.lang.String.format; |
| 8 | + |
| 9 | +/** |
| 10 | + * |
| 11 | + * A iterative version of a ternary search algorithm |
| 12 | + * This is better way to implement the ternary search, because a recursive version adds some overhead to a stack. |
| 13 | + * But in java the compile can transform the recursive version to iterative implicitly, |
| 14 | + * so there are no much differences between these two algorithms |
| 15 | + * |
| 16 | + * Worst-case performance Θ(log3(N)) |
| 17 | + * Best-case performance O(1) |
| 18 | + * Average performance Θ(log3(N)) |
| 19 | + * Worst-case space complexity O(1) |
| 20 | + * |
| 21 | + * |
| 22 | + * @author Podshivalov Nikita (https://github.com/nikitap492) |
| 23 | + * @since 2018-04-13 |
| 24 | + * |
| 25 | + * @see SearchAlgorithm |
| 26 | + * @see TernarySearch |
| 27 | + * |
| 28 | + */ |
| 29 | + |
| 30 | +public class IterativeTernarySearch implements SearchAlgorithm { |
| 31 | + |
| 32 | + |
| 33 | + @Override |
| 34 | + public <T extends Comparable<T>> int find(T[] array, T key) { |
| 35 | + int left = 0; |
| 36 | + int right = array.length - 1; |
| 37 | + while (true) { |
| 38 | + int leftCmp = array[left].compareTo(key); |
| 39 | + int rightCmp = array[right].compareTo(key); |
| 40 | + if (leftCmp == 0) return left; |
| 41 | + if (rightCmp == 0) return right; |
| 42 | + |
| 43 | + int leftThird = left + (right - left) / 3; |
| 44 | + int rightThird = right - (right - left) /3; |
| 45 | + |
| 46 | + if (array[leftThird].compareTo(key) <= 0) left = leftThird; |
| 47 | + else right = rightThird; |
| 48 | + } |
| 49 | + |
| 50 | + } |
| 51 | + |
| 52 | + |
| 53 | + public static void main(String[] args) { |
| 54 | + //just generate data |
| 55 | + Random r = new Random(); |
| 56 | + int size = 100; |
| 57 | + int maxElement = 100000; |
| 58 | + Integer[] integers = Stream.generate(() -> r.nextInt(maxElement)).limit(size).sorted().toArray(Integer[]::new); |
| 59 | + |
| 60 | + |
| 61 | + //the element that should be found |
| 62 | + Integer shouldBeFound = integers[r.nextInt(size - 1)]; |
| 63 | + |
| 64 | + IterativeTernarySearch search = new IterativeTernarySearch(); |
| 65 | + int atIndex = search.find(integers, shouldBeFound); |
| 66 | + |
| 67 | + System.out.println(format("Should be found: %d. Found %d at index %d. An array length %d" |
| 68 | + , shouldBeFound, integers[atIndex], atIndex, size)); |
| 69 | + |
| 70 | + int toCheck = Arrays.binarySearch(integers, shouldBeFound); |
| 71 | + System.out.println(format("Found by system method at an index: %d. Is equal: %b", toCheck, toCheck == atIndex)); |
| 72 | + |
| 73 | + } |
| 74 | + |
| 75 | + |
| 76 | +} |
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