diff --git a/src/main/java/com/thealgorithms/dynamicprogramming/LongestIncreasingSubsequenceNLogN.java b/src/main/java/com/thealgorithms/dynamicprogramming/LongestIncreasingSubsequenceNLogN.java new file mode 100644 index 000000000000..7bc0855e0566 --- /dev/null +++ b/src/main/java/com/thealgorithms/dynamicprogramming/LongestIncreasingSubsequenceNLogN.java @@ -0,0 +1,75 @@ +package com.thealgorithms.dynamicprogramming; + +/** + * Implementation of the Longest Increasing Subsequence (LIS) problem using + * an O(n log n) dynamic programming solution enhanced with binary search. + * + * @author Vusal Huseynov (https://github.com/huseynovvusal) + */ +public final class LongestIncreasingSubsequenceNLogN { + private LongestIncreasingSubsequenceNLogN() { + } + + /** + * Finds the index of the smallest element in the array that is greater than + * or equal to the target using binary search. The search is restricted to + * the first `size` elements of the array. + * + * @param arr The array to search in (assumed to be sorted up to `size`). + * @param size The number of valid elements in the array. + * @param target The target value to find the lower bound for. + * @return The index of the lower bound. + */ + private static int lowerBound(int[] arr, int target, int size) { + int l = 0; + int r = size; + + while (l < r) { + int mid = l + (r - l) / 2; + + if (target > arr[mid]) { + // Move right if target is greater than mid element + l = mid + 1; + } else { + // Move left if target is less than or equal to mid element + r = mid; + } + } + + // Return the index where the target can be inserted + return l; + } + + /** + * Calculates the length of the Longest Increasing Subsequence (LIS) in the given array. + * + * @param arr The input array of integers. + * @return The length of the LIS. + */ + public static int lengthOfLIS(int[] arr) { + if (arr == null || arr.length == 0) { + return 0; // Return 0 for empty or null arrays + } + + // tails[i] - the smallest end element of an increasing subsequence of length i+1 + int[] tails = new int[arr.length]; + // size - the length of the longest increasing subsequence found so far + int size = 0; + + for (int x : arr) { + // Find the position to replace or extend the subsequence + int index = lowerBound(tails, x, size); + + // Update the tails array with the current element + tails[index] = x; + + // If the element extends the subsequence, increase the size + if (index == size) { + size++; + } + } + + // Return the length of the LIS + return size; + } +} diff --git a/src/test/java/com/thealgorithms/dynamicprogramming/LongestIncreasingSubsequenceNLogNTest.java b/src/test/java/com/thealgorithms/dynamicprogramming/LongestIncreasingSubsequenceNLogNTest.java new file mode 100644 index 000000000000..dc87d6751460 --- /dev/null +++ b/src/test/java/com/thealgorithms/dynamicprogramming/LongestIncreasingSubsequenceNLogNTest.java @@ -0,0 +1,22 @@ +package com.thealgorithms.dynamicprogramming; + +import static org.junit.jupiter.api.Assertions.assertEquals; + +import java.util.stream.Stream; +import org.junit.jupiter.params.ParameterizedTest; +import org.junit.jupiter.params.provider.Arguments; +import org.junit.jupiter.params.provider.MethodSource; + +public class LongestIncreasingSubsequenceNLogNTest { + + private static Stream provideTestCases() { + return Stream.of(Arguments.of(new int[] {10, 9, 2, 5, 3, 7, 101, 18}, 4), Arguments.of(new int[] {0, 1, 0, 3, 2, 3}, 4), Arguments.of(new int[] {7, 7, 7, 7, 7}, 1), Arguments.of(new int[] {1, 3, 5, 4, 7}, 4), Arguments.of(new int[] {}, 0), Arguments.of(new int[] {10}, 1), + Arguments.of(new int[] {3, 10, 2, 1, 20}, 3), Arguments.of(new int[] {50, 3, 10, 7, 40, 80}, 4)); + } + + @ParameterizedTest + @MethodSource("provideTestCases") + public void testLengthOfLIS(int[] input, int expected) { + assertEquals(expected, LongestIncreasingSubsequenceNLogN.lengthOfLIS(input)); + } +}