cses/subarray_sum_queries2.cpp at master · RITCHIEsingh/cses · GitHub

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#include <bits/stdc++.h>
//Author : ritchie_s
#define for0(i, n) for (int i = 0; i < (int)(n); ++i) // 0 based indexing
#define for1(i, n) for (int i = 1; i <= (int)(n); ++i) // 1 based indexing
// Short hand for usual tokens
#define pb push_back
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define sp " "
// Shorthand for commonly used types
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef double ld;
// functions
#define MOD 1000000007
ll min(ll a,int b) { if (a<b) return a; return b; }
ll min(int a,ll b) { if (a<b) return a; return b; }
ll max(ll a,int b) { if (a>b) return a; return b; }
ll max(int a,ll b) { if (a>b) return a; return b; }
ll gcd(ll a,ll b) { if (b==0) return a; return gcd(b, a%b); }
ll lcm(ll a,ll b) { return (a/gcd(a,b))*b; }
string to_upper(string a) { for (int i=0;i<(int)a.size();++i) if (a[i]>='a' && a[i]<='z') a[i]-='a'-'A'; return a; }
string to_lower(string a) { for (int i=0;i<(int)a.size();++i) if (a[i]>='A' && a[i]<='Z') a[i]+='a'-'A'; return a; }
bool prime(ll a) { if (a==1) return 0; for (int i=2;i<=round(sqrt(a));++i) if (a%i==0) return 0; return 1; }
// int gcd = __gcd(a,b) , ll LCM = 1LL*a*b/gcd

vll a;

struct node{
    ll sum , pref , suff , ans;
    node(){
        sum = 0 , pref = 0 , suff = 0 , ans = 0;
    }
};

node t[4*200200];

node merge(node L , node R){
    node res;
    res.sum = L.sum + R.sum;
    res.pref = max(L.pref , R.pref+L.sum);
    res.suff = max(R.suff , R.sum+L.suff);
    res.ans = max({L.ans , R.ans , L.suff+R.pref});
    return res;
}

void build(int id , int l , int r){
    if(l==r){
        t[id].ans = a[l] , t[id].pref = a[l] , t[id].suff = a[l] , t[id].sum = a[l];
        return;
    }
    int mid = (l+r)/2;
    build(2*id , l , mid);
    build(2*id+1 , mid+1 , r);
    t[id] = merge(t[2*id] , t[2*id+1]);
}

void update(int id , int l , int r , int idx , int val){
    if(l == r){
        t[id].sum = val , t[id].pref = val , t[id].suff = val , t[id].ans = val;
        return;
    }
    int mid = (l+r)/2;
    if(idx <= mid) update(2*id , l , mid , idx , val);
    else update(2*id+1 , mid+1 , r , idx , val);
    t[id] = merge(t[2*id] , t[2*id+1]);
}

node query(int id , int l , int r , int lq , int rq){
    if(r<lq  ||  l>rq){
        return node();
    }
    if(lq<=l  &&  r<=rq){
        return t[id];
    }
    ll mid = (l+r)/2;
    return merge(query(2*id , l , mid , lq , rq) , query(2*id+1 , mid+1, r , lq , rq));
}


//solver fn
void solve(){
    ll n,m;
    cin>>n>>m;

    a.resize(n);
    for0(i,n){
        cin>>a[i];
    }
    build(1 , 0 , n-1);
    while(m--){
        ll l ,r;
        cin>>l>>r;
        l-- , r--;

        auto ans = query(1 , 0 , n-1 , l , r);
        ll ans_f = ans.ans;
        if(ans_f<0){
            cout<<0<<endl;
        }
        else cout<<ans_f<<endl;
    }
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.precision(10);
    cout << fixed;
     int t=1;

     while(t--){
        solve();
     }
    return 0;
}