(树状数组) AcWing 241. 楼兰图腾

AcWing 241. 楼兰图腾

树状数组

#include<bits/stdc++.h>

using namespace std;
typedef long long LL;
const int N = 2000010;
int n;
int a[N], tr[N];
int Lower[N], Greater[N];


int lowbit(int x) {
    return x & -x;
}

void add(int x, int v) {
    for (int i = x; i < N; i += lowbit(i))tr[i] += v;
}

int get(int x) {
    int res = 0;
    for (int i = x; i; i -= lowbit(i))res += tr[i];
    return res;
}

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

    for (int i = 1; i <= n; i++) {
        int y = a[i];
        Lower[i] = get(y - 1);
        Greater[i] = get(n) - get(y);
        add(y, 1);
    }

    memset(tr, 0, sizeof tr);
    LL res1 = 0, res2 = 0;
    for (int i = n; i >= 1; i--) {
        int y = a[i];
        res1 += Greater[i] * 1ll * (get(n) - get(y));
        res2 += Lower[i] * 1ll * get(y - 1);
        add(y, 1);
    }

    cout << res1 << " " << res2;

    return 0;
}