69 lines
1.7 KiB
Java
69 lines
1.7 KiB
Java
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/*
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* Problem Statement: -
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* Find Longest Alternating Subsequence
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* A sequence {x1, x2, .. xn} is alternating sequence if its elements satisfy one of the following relations :
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x1 < x2 > x3 < x4 > x5 < …. xn or
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x1 > x2 < x3 > x4 < x5 > …. xn
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*/
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import java.io.*;
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public class LongestAlternatingSubsequence {
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/* Function to return longest alternating subsequence length*/
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static int AlternatingLength(int arr[], int n){
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/*
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las[i][0] = Length of the longest
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alternating subsequence ending at
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index i and last element is
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greater than its previous element
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las[i][1] = Length of the longest
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alternating subsequence ending at
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index i and last element is
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smaller than its previous
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element
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*/
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int las[][] = new int[n][2]; // las = LongestAlternatingSubsequence
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for (int i = 0; i < n; i++)
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las[i][0] = las[i][1] = 1;
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int result = 1; // Initialize result
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/* Compute values in bottom up manner */
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for (int i = 1; i < n; i++){
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/* Consider all elements as previous of arr[i]*/
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for (int j = 0; j < i; j++){
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/* If arr[i] is greater, then check with las[j][1] */
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if (arr[j] < arr[i] && las[i][0] < las[j][1] + 1)
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las[i][0] = las[j][1] + 1;
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/* If arr[i] is smaller, then check with las[j][0]*/
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if( arr[j] > arr[i] && las[i][1] < las[j][0] + 1)
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las[i][1] = las[j][0] + 1;
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}
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/* Pick maximum of both values at index i */
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if (result < Math.max(las[i][0], las[i][1]))
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result = Math.max(las[i][0], las[i][1]);
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}
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return result;
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}
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public static void main(String[] args)
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{
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int arr[] = { 10, 22, 9, 33, 49,50, 31, 60 };
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int n = arr.length;
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System.out.println("Length of Longest "+"alternating subsequence is " +AlternatingLength(arr, n));
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}
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}
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