Submission #349380

#	Time	Username	Problem	Language	Result	Execution time	Memory
349380		phathnv	Mountains (NOI20_mountains)	C++11	100 / 100	120 ms	10732 KiB

Mountains

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N = 3e5 + 1;

struct FenwickTree{
    int d[N];
    void update(int x){
        for(; x < N; x += x & -x)
            d[x]++;
    }
    int get(int x){
        int res = 0;
        for(; x > 0; x -= x & -x)
            res += d[x];
        return res;
    }
    int getRange(int l, int r){
        assert(l <= r);
        return get(r) - get(l - 1);
    }
} bit;

int n, ind[N];
ll a[N];

void ReadInput(){
    cin >> n;
    for(int i = 1; i <= n; i++)
        cin >> a[i];
}

void Solve(){
    for(int i = 1; i <= n; i++)
        ind[i] = i;
    sort(ind + 1, ind + 1 + n, [&](const int &x, const int &y){
            return a[x] < a[y];
         });
    ll res = 0;
    for(int i = 1; i <= n; i++){
        int j = i;
        while (j < n && a[ind[i]] == a[ind[j + 1]])
            j++;
        for(int k = i; k <= j; k++)
            res += (ll) bit.getRange(1, ind[k]) * bit.getRange(ind[k], n);
        for(int k = i; k <= j; k++)
            bit.update(ind[k]);
        i = j;
    }

    cout << res;
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    ReadInput();
    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