Submission #1260269

#	Time	Username	Problem	Language	Result	Execution time	Memory
1260269		tminh	Mountains (NOI20_mountains)	C++20	24 / 100	82 ms	3616 KiB

Mountains

#include "bits/stdc++.h"
using namespace std;

#define task ""
#define ll long long
#define endl '\n'
#define fi first
#define se second
#define vall(a) (a).begin(), (a).end()
#define sze(a) (int)a.size()
#define pii pair<int, int>
#define pll pair<ll, ll>


#define ep emplace_back
#define pb push_back
#define pf push_front


const ll mod = 1e9 + 7;
const int N = 1e6 + 5;
const ll oo = 1e18;

bool START;

int n, a[N], m;
vector<int> arr;

struct BIT {
	int bit[N];
	void add(int idx, int delta) {
		for (; idx <= m; idx += idx & -idx) bit[idx] += delta;
	}
	int get(int idx) {
		int res = 0;
		for (; idx > 0; idx -= idx & -idx) res += bit[idx];
		return res;
	}
} bit0, bit1;

inline void solve() {
	sort(vall(arr));
	arr.erase(unique(vall(arr)), arr.end());
	m = sze(arr);
	
	for (int i = 1; i <= n; ++i) {
		a[i] = lower_bound(vall(arr), a[i]) - arr.begin() + 1;
		bit0.add(a[i], 1);
	}
	
	ll ans = 0;
	for (int i = 1; i <= n; ++i) {
		bit0.add(a[i], -1);
		ans += 1ll * bit0.get(a[i] - 1) * bit1.get(a[i] - 1);
		bit1.add(a[i], 1);
	}
	cout << ans;
	
}


inline void input() {
    cin >> n;
    for (int i = 1; i <= n; ++i) {
    	cin >> a[i];
    	arr.pb(a[i]);
    }
    return solve();
}
bool END;

int main() {
    if(fopen(task ".inp", "r")) {
        freopen(task ".inp", "r", stdin);
        freopen(task ".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);

    input();
    
    
    cerr << endl << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << 's' << endl;
    cerr << "Memory: " << fabs ((&END - &START)) / 1048576.0 << "MB\n";
    return 0;
}

Compilation message (stderr)

Mountains.cpp: In function 'int main()':
Mountains.cpp:74:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   74 |         freopen(task ".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
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(task ".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 0 / 36
• Subtask 5: 0 / 28
• Subtask 6: 9 / 9
• Subtask 7: 0 / 12