Given an array of positive numbers, find the maximum subsequence sum <= given sum, such that no two elements are adjacent to each other

问题

This is my code

It passes for few cases but not for all, for eg.

number of elements n = 6

elements a[n] = {5,5,10,100,10,5}

and sum = 25

the output is 15, but output should be 25 (5 + 10 + 10)

click here to see its working in IDE

#include<bits/stdc++.h>
#define ll long long int
using namespace std;
int main(){
    int n;
    ll sum;
    vector<ll> v;
    cin>>n;
    ll a[n];
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    cin>>sum;
    ll ans = 0;
    ll inc = a[0];
    ll exc = 0;
    ll prev = 0;
    for(int i=1;i<n;i++){
        prev = inc;
        inc = max(exc+a[i],a[i]);
        exc = max(prev,exc);
       // cout<<inc<<" "<<exc<<endl;
       ll ans1 = max(inc,exc);
       if(ans1<=sum){
           ans = max(ans1,ans);
       }
    }
    cout<<ans<<endl;
    return 0;
}

来源：https://stackoverflow.com/questions/58824571/given-an-array-of-positive-numbers-find-the-maximum-subsequence-sum-given-su