Submission #795596

#	Time	Username	Problem	Language	Result	Execution time	Memory
795596		stefanneagu	Mountains (NOI20_mountains)	C++17	100 / 100	572 ms	34064 KiB

Mountains

#include <iostream>
#include <map>
#define int long long

using namespace std;

const int nmax = 3e5 + 7;
int dr[nmax], st[nmax], f[nmax], v[nmax];
map<int, int> mp;

void update(int i) {
    int val = 1;
    while(i < nmax) {
        f[i] += val;
        i += (i & (-i));
    }
}

int query(int i) {
    int sum = 0;
    while(i > 0) {
        sum += f[i];
        i -= (i & (-i));
    }
    return sum;
}

int32_t main() {
    int n;
    cin >> n;
    for(int i = 1; i <= n; i ++) {
        cin >> v[i];
        mp[v[i]];
    }
    int cnt = 2;
    for(auto &it : mp) {
        it.second = cnt;
        cnt ++;
    }
    for(int i = 1; i <= n; i ++) {
        v[i] = mp[v[i]];
    }
    for(int i = 1; i <= n; i ++) {
        dr[i] = query(v[i] - 1);
        update(v[i]);
    }
    for(int i = 0; i < nmax; i ++) {
        f[i] = 0;
    }
    for(int i = n; i >= 1; i --) {
        st[i] = query(v[i] - 1);
        update(v[i]);
    }
    long long ans = 0;
    for(int i = 1; i <= n;  i ++) {
        ans += dr[i] * st[i];
    } 
    cout << ans;
    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