Shared code

/*
  author: @ankingcodes
  created: 2021-07-20 13:55:39.959135
*/
        
#include<bits/stdc++.h>
#include<algorithm>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;
#define ll long long
#define INF 1e18
#define MOD 1000000007

typedef tree<int, null_type, less<int>, rb_tree_tag,
                tree_order_statistics_node_update> PBDS;

typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag,
                tree_order_statistics_node_update> pairPBDS;

int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll n, a, b; cin >> n >> a >> b;
  vector<ll> pf(n+1);
  for (int i=1;i<=n;i++){
    ll x; cin >> x;
    pf[i] = pf[i-1] + x;
  }
  set<ll> s;
  for (int i=a;i<=b;i++) 
    s.insert(pf[i]);
  ll mxs = -INF;
  for (int i=1;i<=n-a+1;i++) {
    mxs = max(mxs, *s.rbegin() - pf[i-1]);
    s.erase(pf[i+a-1]);
    if (i + b <= n) 
      s.insert(pf[i+b]);
  }
  cout << mxs << endl;
  return 0;
}