# Maximum sum such that no two elements are adjacent | Set 2

• Difficulty Level : Medium
• Last Updated : 24 Nov, 2021

Given an array of positive numbers, find the maximum sum of a subsequence with the constraint that no 2 numbers in the sequence should be adjacent in the array. So 3 2 7 10 should return 13 (sum of 3 and 10) or 3 2 5 10 7 should return 15 (sum of 3, 5, and 7).

Examples:

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```Input :  arr[] = {3, 5, 3}
Output : 6
Explanation :
Selecting indexes 0 and 2 will maximise the sum
i.e 3+3 = 6

Input : arr[] = {2, 5, 2}
Output : 5 ```

We have already discussed the efficient approach of solving this problem in the previous article.
However, we can also solve this problem using the Dynamic Programming approach.
Dynamic Programming Approach: Let’s decide the states of ‘dp’. Let dp[i] be the largest possible sum for the sub-array starting from index ‘i’ and ending at index ‘N-1’. Now, we have to find a recurrence relation between this state and a lower-order state.
In this case for an index ‘i’, we will have two choices.

```1) Choose the current index:
In this case, the relation will be dp[i] = arr[i] + dp[i+2]
2) Skip the current index:
Relation will be dp[i] = dp[i+1]```

We will choose the path that maximizes our result.
Thus, the final relation will be:

`dp[i] = max(dp[i+2]+arr[i], dp[i+1])`

Below is the implementation of the above approach:

## C++

 `// C++ program to implement above approach` `#include ``#define maxLen 10``using` `namespace` `std;` `// variable to store states of dp``int` `dp[maxLen];` `// variable to check if a given state``// has been solved``bool` `v[maxLen];` `// Function to find the maximum sum subsequence``// such that no two elements are adjacent``int` `maxSum(``int` `arr[], ``int` `i, ``int` `n)``{``    ``// Base case``    ``if` `(i >= n)``        ``return` `0;` `    ``// To check if a state has``    ``// been solved``    ``if` `(v[i])``        ``return` `dp[i];``    ``v[i] = 1;` `    ``// Required recurrence relation``    ``dp[i] = max(maxSum(arr, i + 1, n),``                ``arr[i] + maxSum(arr, i + 2, n));` `    ``// Returning the value``    ``return` `dp[i];``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 12, 9, 7, 33 };` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``);` `    ``cout << maxSum(arr, 0, n);` `    ``return` `0;``}`

## Java

 `// Java program to implement above approach``class` `GFG``{` `static` `int` `maxLen = ``10``;` `// variable to store states of dp``static` `int` `dp[] = ``new` `int``[maxLen];` `// variable to check if a given state``// has been solved``static` `boolean` `v[] = ``new` `boolean``[maxLen];` `// Function to find the maximum sum subsequence``// such that no two elements are adjacent``static` `int` `maxSum(``int` `arr[], ``int` `i, ``int` `n)``{``    ``// Base case``    ``if` `(i >= n)``        ``return` `0``;` `    ``// To check if a state has``    ``// been solved``    ``if` `(v[i])``        ``return` `dp[i];``    ``v[i] = ``true``;` `    ``// Required recurrence relation``    ``dp[i] = Math.max(maxSum(arr, i + ``1``, n),``                ``arr[i] + maxSum(arr, i + ``2``, n));` `    ``// Returning the value``    ``return` `dp[i];``}` `// Driver code``public` `static` `void` `main(String args[])``{``    ``int` `arr[] = { ``12``, ``9``, ``7``, ``33` `};``    ``int` `n = arr.length;``    ``System.out.println( maxSum(arr, ``0``, n));``}``}` `// This code is contributed by Arnab Kundu`

## Python3

 `# Python 3 program to implement above approach``maxLen ``=` `10` `# variable to store states of dp``dp ``=` `[``0` `for` `i ``in` `range``(maxLen)]` `# variable to check if a given state``# has been solved``v ``=` `[``0` `for` `i ``in` `range``(maxLen)]` `# Function to find the maximum sum subsequence``# such that no two elements are adjacent``def` `maxSum(arr, i, n):``    ``# Base case``    ``if` `(i >``=` `n):``        ``return` `0` `    ``# To check if a state has``    ``# been solved``    ``if` `(v[i]):``        ``return` `dp[i]``    ``v[i] ``=` `1` `    ``# Required recurrence relation``    ``dp[i] ``=` `max``(maxSum(arr, i ``+` `1``, n),``            ``arr[i] ``+` `maxSum(arr, i ``+` `2``, n))` `    ``# Returning the value``    ``return` `dp[i]` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``12``, ``9``, ``7``, ``33``]` `    ``n ``=` `len``(arr)``    ``print``(maxSum(arr, ``0``, n))` `# This code is contributed by``# Surendra_Gangwar`

## C#

 `// C# program to implement above approach``using` `System;` `class` `GFG``{` `static` `int` `maxLen = 10;` `// variable to store states of dp``static` `int``[] dp = ``new` `int``[maxLen];` `// variable to check if a given state``// has been solved``static` `bool``[] v = ``new` `bool``[maxLen];` `// Function to find the maximum sum subsequence``// such that no two elements are adjacent``static` `int` `maxSum(``int``[] arr, ``int` `i, ``int` `n)``{``    ``// Base case``    ``if` `(i >= n)``        ``return` `0;` `    ``// To check if a state has``    ``// been solved``    ``if` `(v[i])``        ``return` `dp[i];``    ``v[i] = ``true``;` `    ``// Required recurrence relation``    ``dp[i] = Math.Max(maxSum(arr, i + 1, n),``                ``arr[i] + maxSum(arr, i + 2, n));` `    ``// Returning the value``    ``return` `dp[i];``}` `// Driver code``public` `static` `void` `Main()``{``    ``int``[] arr = { 12, 9, 7, 33 };``    ``int` `n = arr.Length;``    ``Console.Write( maxSum(arr, 0, n));``}``}` `// This code is contributed by ChitraNayal`

## PHP

 `= ``\$n``)``        ``return` `0;` `    ``// To check if a state has``    ``// been solved``    ``if` `(``\$GLOBALS``[``'v'``][``\$i``])``        ``return` `\$GLOBALS``[``'dp'``][``\$i``];``        ` `    ``\$GLOBALS``[``'v'``][``\$i``] = 1;` `    ``// Required recurrence relation``    ``\$GLOBALS``[``'dp'``][``\$i``] = max(maxSum(``\$arr``, ``\$i` `+ 1, ``\$n``),``                ``\$arr``[``\$i``] + maxSum(``\$arr``, ``\$i` `+ 2, ``\$n``));` `    ``// Returning the value``    ``return` `\$GLOBALS``[``'dp'``][``\$i``];``}` `    ``// Driver code``    ``\$arr` `= ``array``( 12, 9, 7, 33 );` `    ``\$n` `= ``count``(``\$arr``);` `    ``echo` `maxSum(``\$arr``, 0, ``\$n``);` `    ``// This code is contributed by AnkitRai01``?>`

## Javascript

 ``
Output:
`45`

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