Submission #1066311

#	Time	Username	Problem	Language	Result	Execution time	Memory
1066311		tamthegod	Mountains (NOI20_mountains)	C++17	100 / 100	171 ms	19176 KiB

Mountains

#include<bits/stdc++.h>

#define int long long
#define pb push_back
#define fi first
#define se second
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxN = 1e6 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;
int n, a[maxN];
vector<int> vc;
struct BIT
{
    vector<int> bit;
    int n;
    void init(int _n)
    {
        n = _n;
        bit.resize(n + 5, 0);
    }
    void update(int pos, int val)
    {
        for(; pos <= n; pos += (pos & (-pos)))
            bit[pos] += val;
    }
    int get(int pos)
    {
        int res = 0;
        for(; pos; pos -= (pos & (-pos)))
            res += bit[pos];
        return res;
    }
};
void ReadInput()
{
    cin >> n;
    for(int i=1; i<=n; i++)
    {
        cin >> a[i];
        vc.pb(a[i]);
    }
    sort(vc.begin(), vc.end());
    vc.erase(unique(vc.begin(), vc.end()), vc.end());
    for(int i=1; i<=n; i++)
        a[i] = upper_bound(vc.begin(), vc.end(), a[i]) - vc.begin();

}
void Solve()
{
    BIT pref, suff;
    pref.init(n);
    suff.init(n);
    for(int i=2; i<=n; i++)
        suff.update(a[i], 1);
    pref.update(a[1], 1);
    int res = 0;
    for(int i=2; i<n; i++)
    {
        suff.update(a[i], - 1);
        res += pref.get(a[i] - 1) * suff.get(a[i] - 1);
        pref.update(a[i], 1);
    }
    cout << res;
}
#define taskname ""
int32_t main()
{
    if (fopen(taskname ".inp", "r"))
    {
        freopen(taskname ".inp", "r", stdin);
        freopen(taskname ".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    //cin >> T;
    for(int itest=1; itest<=T; itest++)
    {
        ReadInput();
        Solve();
    }
}

Compilation message (stderr)

Mountains.cpp: In function 'int32_t main()':
Mountains.cpp:75:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   75 |         freopen(taskname ".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Mountains.cpp:76:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   76 |         freopen(taskname ".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• 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