P3157 动态逆序对

#include <bits/stdc++.h>
#define LL long long
using namespace std;

const int N = 100010;
int sum[N * 400], lc[N * 400], rc[N * 400];
int root[N], cnt;
int n, m;
int A[N], R[N];
LL ans;

LL T_ask(int p, int l, int r, int x, int y) 
{
    if(x <= l && r <= y) return (LL)sum[p];
    if(p == 0 || sum[p] == 0) return 0;
    int mid = l + r >> 1;
    LL ans = 0;
    if(x <= mid) ans += T_ask(lc[p], l, mid, x, y);
    if(y > mid)  ans += T_ask(rc[p], mid + 1, r, x, y);
    return ans;
}

LL ask(int p, int k) 
{
    LL ans = 0;
    while(p > 0)
    {
        ans += T_ask(root[p], 1, n, 1, k);
        p -= p & -p;
    }     
    return ans;
}

int Tadd(int p, int l, int r, int k) 
{
    int rt = p;
    if(!rt) rt = ++cnt;
    ++sum[rt];
    if(l == r) return rt;
    int mid = l + r >> 1;
    if(k <= mid) lc[rt] = Tadd(lc[rt], l, mid, k);
    if(k > mid) rc[rt] = Tadd(rc[rt], mid + 1, r, k);
    return rt;
}

void Add(int p, int k) 
{
    while(p <= n) {
        root[p] = Tadd(root[p], 1, n, k);
        p += p & -p;
    }
}

int tdel(int p, int l, int r, int k) 
{
    if(p == 0) return p;
    --sum[p];
    if(sum[p] == 0) return 0; //如果已经为0，不如干脆删掉
    if(l == r) return p;
    int mid = l + r >> 1;
    if(k <= mid) tdel(lc[p], l, mid, k);
    if(k > mid) tdel(rc[p], mid + 1, r, k);
    return p;
}

void del(int p, int k) 
{
    while(p <= n) {
        root[p] = tdel(root[p], 1, n, k);
        p += p & -p;
    }
}

int main() 
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n >> m;
    for(int i = 1; i <= n; i++) 
    {
        cin >> A[i];
        R[A[i]] = i;
        ans += ask(i - 1, A[i]);
        Add(i, A[i]);
    }

    ans = 1ll * n * (n - 1) / 2 - ans;
    cout << ans << '\n';
    for(int i = 1; i < m; i++) 
    {
        int x; 
        cin >> x;
        ans -= ask(R[x], n) + ask(n, x) - 2 * ask(R[x], x); 
        del(R[x], x);
        cout << ans << '\n';
    }
    return 0;
}