Submission #680895

#	Time	Username	Problem	Language	Result	Execution time	Memory
680895		DennisTran	Mountains (NOI20_mountains)	C++17	100 / 100	161 ms	14340 KiB

Mountains

#pragma GCC optimize("O2")
#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FOD(i, a, b) for (int i = (a); i >= (b); i--)
#define REP(i, n) for (int i = 0; i < (n); i++)
#define ALL(x) (x).begin(), (x).end()
#define TIME  (1.0 * clock() / CLOCKS_PER_SEC)
#define file(name)  if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }

using namespace std;

const int MAXN = 3e5 + 5;

int N, L[MAXN], R[MAXN];
vector <long long> nen;
long long a[MAXN];

struct BIT{
    int bit[MAXN];
    void upd(int x, int val) {for (; x <= N; x += x &-x) bit[x] += val;}
    int get(int x) {
        int ans = 0;
        for (; x; x -= x&-x) ans += bit[x];
        return ans;
    }
} mybit;

void calc(int *val) {
    FOR(i, 1, N) {
        val[i] = mybit.get(a[i] - 1);
        mybit.upd(a[i], 1);
    }
    FOR(i, 1, N) {
        mybit.upd(a[i], -1);
    }
}

signed main(void) {
    ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
    //file("TASK");
    cin >> N;
    FOR(i, 1, N) cin >> a[i], nen.emplace_back(a[i]);
    sort(ALL(nen)); nen.erase(unique(ALL(nen)), nen.end());
    FOR(i, 1, N) a[i] = lower_bound(ALL(nen), a[i]) - nen.begin() + 1;

    calc(L);
    reverse(a + 1, a + N + 1);
    calc(R);
    reverse(R + 1, R + N + 1);
    long long ans = 0;
    FOR(i, 1, N) ans += 1ll * L[i] * R[i];
    cout << ans;
    cerr << "Time elapsed: " << TIME << " s.\n";
    return (0 ^ 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