CSES – Maximum Subarray Sum II

#include<bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define f first
#define s second
#define fastio ios_base::sync_with_stdio(0);cin.tie(0)
using namespace std;
//declare
int n,a,b;
vector<int> pre;
multiset<int> st;
//
signed main(){
    fastio;
    cin>>n>>a>>b;
    pre.push_back(0);
    for(int i=0;i<n;i++){
        int x; cin>>x;
        pre.push_back(pre.back() + x);
    }
    int ans = -1e18;
    for(int i=0;i<=n;i++){
        if(st.size()) ans = max(ans, pre[i]-*st.begin());
        if(i-b >= 0) st.erase(st.find(pre[i-b]));
        if(i-a+1 >= 0) st.insert(pre[i-a+1]);
    }
    cout<<ans<<"\n";
    return 0;
}