Merge pull request #167 from NarenCK11/altsubseq

Added Longest Alternating Subsequence problem in Java

Author: admirerr

Java/dynamic-programming/LongestAlternatingSubsequence.java

@@ -0,0 +1,49 @@
+import java.util.Arrays;
+
+public final class LongestAlternatingSubsequence {
+    private LongestAlternatingSubsequence() {
+    }
+
+    static int alternatingLength(int[] arr, int n) {
+        if (n == 0) {
+            return 0;
+        }
+
+        int[][] las = new int[n][2];
+
+        for (int i = 0; i < n; i++) {
+            las[i][0] = 1;
+            las[i][1] = 1;
+        }
+
+        int result = 1;
+
+        for (int i = 1; i < n; i++) {
+            for (int j = 0; j < i; j++) {
+                if (arr[j] < arr[i] && las[i][0] < las[j][1] + 1) {
+                    las[i][0] = las[j][1] + 1;
+                }
+
+                if (arr[j] > arr[i] && las[i][1] < las[j][0] + 1) {
+                    las[i][1] = las[j][0] + 1;
+                }
+            }
+            result = Math.max(result, Math.max(las[i][0], las[i][1]));
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        int[] arr1 = {10, 22, 9, 33, 49, 50, 31, 60};
+        int length1 = alternatingLength(arr1, arr1.length);
+        System.out.println("Array: " + Arrays.toString(arr1));
+        System.out.println("Length of the longest alternating subsequence is: " + length1);
+
+        System.out.println("\n----------------------------------------\n");
+
+        int[] arr2 = {1, 5, 4, 8, 2, 7, 3};
+        int length2 = alternatingLength(arr2, arr2.length);
+        System.out.println("Array: " + Arrays.toString(arr2));
+        System.out.println("Length of the longest alternating subsequence is: " + length2);
+    }
+}