제출 #1224363

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1224363		vipul	Group Photo (JOI21_ho_t3)	C++20	0 / 100	0 ms	320 KiB

Main

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

struct Fenwick {
    int n;
    vector<ll> f;
    Fenwick(int _n): n(_n), f(n+1, 0) {}
    void update(int i, ll v) {
        for (; i <= n; i += i&-i) f[i] += v;
    }
    ll query(int i) {
        ll s = 0;
        for (; i > 0; i -= i&-i) s += f[i];
        return s;
    }
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N;
    cin >> N;
    vector<ll> B(N);
    for(int i = 0; i < N; i++){
        ll a;
        cin >> a;
        B[i] = a + 2LL * i;
    }

    // Coordinate‐compress B so we can index the Fenwick tree
    vector<ll> vals = B;
    sort(vals.begin(), vals.end());
    vals.erase(unique(vals.begin(), vals.end()), vals.end());

    Fenwick fw(vals.size());
    ll ans = 0;

    // We iterate left-to-right; at each B[i], we want
    //   # of previous B[j] > B[i] = total_seen - # of previous ≤ B[i]
    for(int i = 0; i < N; i++){
        int pos = int(lower_bound(vals.begin(), vals.end(), B[i]) - vals.begin()) + 1;
        ll seen_le = fw.query(pos);
        ll seen_tot = i; 
        ans += (seen_tot - seen_le);
        fw.update(pos, 1);
    }

    cout << ans << "\n";
    return 0;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 7
• Subtask 3: 0 / 32
• Subtask 4: 0 / 20
• Subtask 5: 0 / 36