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Maximum sum Bi-tonic Sub-sequence

Given an array of integers. A subsequence of arr[] is called Bitonic if it is first increasing, then decreasing.

Examples :

Input : arr[] = {1, 15, 51, 45, 33, 
                   100, 12, 18, 9}
Output : 194
Explanation : Bi-tonic Sub-sequence are :
             {1, 51, 9} or {1, 50, 100, 18, 9} or
             {1, 15, 51, 100, 18, 9}  or 
             {1, 15, 45, 100, 12, 9}  or 
             {1, 15, 45, 100, 18, 9} .. so on            
Maximum sum Bi-tonic sub-sequence is 1 + 15 +
51 + 100 + 18 + 9 = 194   

Input : arr[] = {80, 60, 30, 40, 20, 10} 
Output : 210  



This problem is a variation of standard Longest Increasing Subsequence (LIS) problem and longest Bitonic Sub-sequence.

We construct two arrays MSIBS[] and MSDBS[]. MSIBS[i] stores the sum of the Increasing subsequence ending with arr[i]. MSDBS[i] stores the sum of the Decreasing subsequence starting from arr[i]. Finally, we need to return the max sum of MSIBS[i] + MSDBS[i] – Arr[i].

Below is the implementation of above idea

C/C++

// C++ program to find maximum sum of bi-tonic sub-sequence
#include <bits/stdc++.h>
using namespace std;
  
// Function return maximum sum of Bi-tonic sub-sequence
int MaxSumBS(int arr[], int n)
{
    int max_sum = INT_MIN;
  
    // MSIBS[i] ==> Maximum sum Increasing Bi-tonic
    // subsequence ending with arr[i]
    // MSDBS[i] ==> Maximum sum Decreasing Bi-tonic
    // subsequence starting with arr[i]
    // Initialize MSDBS and MSIBS values as arr[i] for
    // all indexes
    int MSIBS[n], MSDBS[n];
    for (int i = 0; i < n; i++) {
        MSDBS[i] = arr[i];
        MSIBS[i] = arr[i];
    }
  
    // Compute MSIBS values from left to right */
    for (int i = 1; i < n; i++)
        for (int j = 0; j < i; j++)
            if (arr[i] > arr[j] && MSIBS[i] < MSIBS[j] + arr[i])
                MSIBS[i] = MSIBS[j] + arr[i];
  
    // Compute MSDBS values from right to left
    for (int i = n - 2; i >= 0; i--)
        for (int j = n - 1; j > i; j--)
            if (arr[i] > arr[j] && MSDBS[i] < MSDBS[j] + arr[i])
                MSDBS[i] = MSDBS[j] + arr[i];
  
    // Find the maximum value of MSIBS[i] + MSDBS[i] - arr[i]
    for (int i = 0; i < n; i++)
        max_sum = max(max_sum, (MSDBS[i] + MSIBS[i] - arr[i]));
  
    // return max sum of bi-tonic sub-sequence
    return max_sum;
}
  
// Driver program
int main()
{
    int arr[] = { 1, 15, 51, 45, 33, 100, 12, 18, 9 };
    int n = sizeof(arr) / sizeof(arr[0]);
    cout << "Maximum Sum : " << MaxSumBS(arr, n);
  
    return 0;
}

Java

// java program to find maximum
// sum of bi-tonic sub-sequence
import java.io.*;
  
class GFG {
  
    // Function return maximum sum
    // of Bi-tonic sub-sequence
    static int MaxSumBS(int arr[], int n)
    {
        int max_sum = Integer.MIN_VALUE;
  
        // MSIBS[i] ==> Maximum sum Increasing Bi-tonic
        // subsequence ending with arr[i]
        // MSDBS[i] ==> Maximum sum Decreasing Bi-tonic
        // subsequence starting with arr[i]
        // Initialize MSDBS and MSIBS values as arr[i] for
        // all indexes
        int MSIBS[] = new int[n];
        int MSDBS[] = new int[n];
        for (int i = 0; i < n; i++) {
            MSDBS[i] = arr[i];
            MSIBS[i] = arr[i];
        }
  
        // Compute MSIBS values from left to right */
        for (int i = 1; i < n; i++)
            for (int j = 0; j < i; j++)
                if (arr[i] > arr[j] && MSIBS[i] < MSIBS[j] + arr[i])
                    MSIBS[i] = MSIBS[j] + arr[i];
  
        // Compute MSDBS values from right to left
        for (int i = n - 2; i >= 0; i--)
            for (int j = n - 1; j > i; j--)
                if (arr[i] > arr[j] && MSDBS[i] < MSDBS[j] + arr[i])
                    MSDBS[i] = MSDBS[j] + arr[i];
  
        // Find the maximum value of MSIBS[i] +
        // MSDBS[i] - arr[i]
        for (int i = 0; i < n; i++)
            max_sum = Math.max(max_sum, (MSDBS[i] + MSIBS[i] - arr[i]));
  
        // return max sum of bi-tonic
        // sub-sequence
        return max_sum;
    }
  
    // Driver program
    public static void main(String[] args)
    {
        int arr[] = { 1, 15, 51, 45, 33, 100, 12, 18, 9 };
        int n = arr.length;
        System.out.println("Maximum Sum : " + MaxSumBS(arr, n));
    }
}
  
// This code is contributed by vt_m

Python

# Dynamic Programming implementation of maximum sum of bitonic subsequence 
  
# Function return maximum sum of Bi-tonic sub-sequence
def max_sum(arr, n):
  
    # MSIBS[i] ==> Maximum sum Increasing Bi-tonic
    # subsequence ending with arr[i]
    # MSDBS[i] ==> Maximum sum Decreasing Bi-tonic
    # subsequence starting with arr[i]
  
    # allocate memory for MSIBS and initialize it to arr[i] for
    # all indexes
    MSIBS = arr[:]
  
    # Compute MSIBS values from left to right
    for i in range(n):
  
        for j in range(0, i):
  
            if arr[i] > arr[j] and MSIBS[i] < MSIBS[j] + arr[i]:
  
                MSIBS[i] = MSIBS[j] + arr[i]
  
    # allocate memory for MSDBS and initialize it to arr[i] for
    # all indexes
    MSDBS = arr[:]
  
    # Compute MSDBS values from right to left
    for i in range(1, n + 1):
  
        for j in range(1, i):
  
            if arr[-i] > arr[-j] and MSDBS[-i] < MSDBS[-j] + arr[-i]:
      
                MSDBS[-i] = MSDBS[-j] + arr[-i]
  
    max_sum = float("-Inf"
  
    # Find the maximum value of MSIBS[i] + MSDBS[i] - arr[i]
    for i, j, k in zip(MSIBS, MSDBS, arr):
  
        max_sum = max(max_sum, i + j - k)
  
    # return max sum of bi-tonic sub-sequence
    return max_sum
  
  
# Driver program to test the above function
def main():
  
    arr = [1, 15, 51, 45, 33, 100, 12, 18, 9]
  
    n = len(arr)
  
    print max_sum(arr, n)
  
if __name__ == '__main__':
    main()
# This code is contributed by Neelam Yadav

C#

// C# program to find maximum
// sun of bi-tonic sub-sequence
using System;
  
class GFG {
  
    // Function return maximum sum
    // of Bi-tonic sub-sequence
    static int MaxSumBS(int[] arr, int n)
    {
        int max_sum = int.MinValue;
  
        // MSIBS[i] ==> Maximum sum Increasing Bi-tonic
        // subsequence ending with arr[i]
        // MSDBS[i] ==> Maximum sum Decreasing Bi-tonic
        // subsequence starting with arr[i]
        // Initialize MSDBS and MSIBS values as arr[i] for
        // all indexes
        int[] MSIBS = new int[n];
        int[] MSDBS = new int[n];
        for (int i = 0; i < n; i++) {
            MSDBS[i] = arr[i];
            MSIBS[i] = arr[i];
        }
  
        // Compute MSIBS values from left to right */
        for (int i = 1; i < n; i++)
            for (int j = 0; j < i; j++)
                if (arr[i] > arr[j] && MSIBS[i] < MSIBS[j] + arr[i])
                    MSIBS[i] = MSIBS[j] + arr[i];
  
        // Compute MSDBS values from right to left
        for (int i = n - 2; i >= 0; i--)
            for (int j = n - 1; j > i; j--)
                if (arr[i] > arr[j] && MSDBS[i] < MSDBS[j] + arr[i])
                    MSDBS[i] = MSDBS[j] + arr[i];
  
        // Find the maximum value of MSIBS[i] +
        // MSDBS[i] - arr[i]
        for (int i = 0; i < n; i++)
            max_sum = Math.Max(max_sum, (MSDBS[i] + MSIBS[i] - arr[i]));
  
        // return max sum of bi-tonic
        // sub-sequence
        return max_sum;
    }
  
    // Driver program
    public static void Main()
    {
        int[] arr = { 1, 15, 51, 45, 33, 100, 12, 18, 9 };
        int n = arr.Length;
        Console.WriteLine("Maximum Sum : " + MaxSumBS(arr, n));
    }
}
  
// This code is contributed by vt_m

PHP

<?php
// PHP program to find maximum
// sun of bi-tonic sub-sequence
function MaxSumBS($arr, $n)
{
    $max_sum = PHP_INT_MIN;
  
    // MSIBS[i] ==> Maximum sum Increasing 
    // Bi-tonic subsequence ending with arr[i]
    // MSDBS[i] ==> Maximum sum Decreasing 
    // Bi-tonic subsequence starting with arr[i]
    // Initialize MSDBS and MSIBS values
    // as arr[i] for all indexes
    $MSIBS = array();
    $MSDBS = array();
    for ($i = 0; $i < $n; $i++) 
    {
        $MSDBS[$i] = $arr[$i];
        $MSIBS[$i] = $arr[$i];
    }
  
    // Compute MSIBS values
    // from left to right */
    for ($i = 1; $i < $n; $i++)
        for ($j = 0; $j < $i; $j++)
            if ($arr[$i] > $arr[$j] && 
                $MSIBS[$i] < $MSIBS[$j] + 
                             $arr[$i])
                $MSIBS[$i] = $MSIBS[$j] + 
                             $arr[$i];
  
    // Compute MSDBS values 
    // from right to left
    for ($i = $n - 2; $i >= 0; $i--)
        for ($j = $n - 1; $j > $i; $j--)
            if ($arr[$i] > $arr[$j] && 
                $MSDBS[$i] < $MSDBS[$j] + 
                             $arr[$i])
                $MSDBS[$i] = $MSDBS[$j] + 
                             $arr[$i];
  
    // Find the maximum value of
    // MSIBS[i] + MSDBS[i] - arr[i]
    for ($i = 0; $i < $n; $i++)
        $max_sum = max($max_sum, ($MSDBS[$i] + 
                                  $MSIBS[$i] - 
                                  $arr[$i]));
  
    // return max sum of 
    // bi-tonic sub-sequence
    return $max_sum;
}
  
// Driver Code
$arr = array(1, 15, 51, 45, 33, 
             100, 12, 18, 9);
$n = count($arr);
echo "Maximum Sum : "
      MaxSumBS($arr, $n);
  
// This code is contributed
// by shiv_bhakt.
?>


Output:

Maximum Sum : 194

Time complexity : O(n2)

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



This article is attributed to GeeksforGeeks.org

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