Submission #439013

#	Time	Username	Problem	Language	Result	Execution time	Memory
439013		meatrow	Mountains (NOI20_mountains)	C++17	100 / 100	1445 ms	48200 KiB

Mountains

#include <bits/stdc++.h>
 
using namespace std;
 
using ll = long long;
using ld = long double;
 
const int MOD = 998244353;
 
ll binpow(ll a, ll p, int mod = MOD) {
    ll res = 1;
    while (p) {
        if (p & 1) {
            (res *= a) %= mod;
        }
        p >>= 1;
        (a *= a) %= mod;
    }
    return res;
}
 
ll gcd(ll a, ll b) {
    return b == 0 ? a : gcd(b, a % b);
}

const int N = 3e5 + 5;

ll fenw[N];

void add(int pos) {
    for (; pos < N; pos |= pos + 1) {
        fenw[pos]++;
    }
}

ll get(int pos) {
    ll res = 0;
    for (; pos >= 0; pos = (pos & (pos + 1)) - 1) {
        res += fenw[pos];
    }
    return res;
}

void solve() {
    int n;
    cin >> n;
    vector<ll> h(n);
    set<ll> setik;
    for (int i = 0; i < n; i++) {
        cin >> h[i];
        setik.insert(h[i]);
    }
    int cur = 0;
    map<ll, int> id;
    for (ll val : setik) {
        id[val] = cur++;
    }
    vector<ll> l(n), r(n);
    for (int i = 0; i < n; i++) {
        l[i] = get(id[h[i]] - 1);
        add(id[h[i]]);
    }
    fill(fenw, fenw + N, 0);
    for (int i = n - 1; i >= 0; i--) {
        r[i] = get(id[h[i]] - 1);
        add(id[h[i]]);
    }
    ll ans = 0;
    for (int i = 0; i < n; i++) {
        ans += l[i] * r[i];
    }
    cout << ans << endl;
}
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    // cin >> T;
    for (int tc = 1; tc <= T; tc++) {
        // cout << "Case #" << tc << ": ";
        solve();
    }
    return 0;
}

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12