Maximum Sum Such that No Two Elements are Adjacent

Question: Given an array all of whose elements are 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.
Ex-1:  3 2 7 10 should return 13 (sum of 3 and 10) .
Ex-2: 3 2 5 10 7 should return 15 (sum of 3, 5 and 7).

Algorithm:

Loop for all elements in arr[] and maintain two sums incl and excl
where
      incl = Max sum including the previous element and
      excl = Max sum excluding the previous element.

Max sum excluding the current element will be max(incl, excl) and
max sum including the current element will be excl + current element
(Note that only excl is considered because elements cannot be adjacent).

At the end of the loop return max of incl and excl.

Explanation:

  arr[] = {5,  5, 10, 40, 50, 35}

  inc = 5
  exc = 0

  For i = 1 (current element is 5)
  incl =  (excl + arr[i])  = 5
  excl =  max(5, 0) = 5

  For i = 2 (current element is 10)
  incl =  (excl + arr[i]) = 15
  excl =  max(5, 5) = 5

  For i = 3 (current element is 40)
  incl = (excl + arr[i]) = 45
  excl = max(5, 15) = 15

  For i = 4 (current element is 50)
  incl = (excl + arr[i]) = 65
  excl =  max(45, 15) = 45

  For i = 5 (current element is 35)
  incl =  (excl + arr[i]) = 80
  excl = max(5, 15) = 65

And 35 is the last element. So, answer is max(incl, excl) =  80.

C++ Code:

    #include <iostream>

    using namespace std;
     
    int FindMax(int a[],int l){
        int incl=a[0];
        int excl=0;

        for(int i=1;i<l;i++){
            int excl_new=(incl>excl)?incl:excl;
            incl=excl+a[i];
            excl=excl_new;
        }

        return (incl>excl)?incl:excl;
    }
     
    int main(){
        int a[]={3,2,7,10};
        cout<<FindMax(a,4)<<endl;
    }