Fenwick.cpp

#include<bits/stdc++.h>
using namespace std;
#define ll                  long long
#define rep(i,n)            for(ll i=0;i<n;i++)
#define hell                1000000007LL
#define vi                  vector<ll>
#define vii                 vector< vi >
#define pb                  push_back
#define mp                  make_pair
#define fi                  first
#define se                  second
#define pii                 pair<ll,ll>
#define all(c)              c.begin(),c.end()
#define mini(c)             min_element(all(c))
#define maxi(c)             max_element(all(c))
ll fenwick[100001],arr[100001],n;
ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a % b); }
ll lcm(ll a, ll b) { return a * (b / gcd(a, b)); }
ll Max(ll a, ll b) { return a > b ? a : b; }
ll Min(ll a, ll b) { return a < b ? a : b; }
ll power(ll x, ll y,ll p)
{
    ll res=1;
    x=x%p;
    while(y>0)
    {
        if(y&1)
            res=((res%p)*(x%p))%p;
        y=y>>1;
        x=((x%p)*(x%p))%p;
    }
    return res;
}
void update(ll x,ll y)
{
    for(;x<=n;x+=(x&-x))
    {
        fenwick[x]+=y;
    }
}
ll query(ll x)
{
    ll sum=0;
    for(;x>0;x-=(x&-x))
    {
        sum+=fenwick[x];
    }
    return sum;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin>>n;
    rep(i,n)
    {
        cin>>arr[i+1];
        update(i,arr[i]);
    }
    cout<<"[2-7] "<<query(7)-query(2-1)<<endl;
    return 0;
}