bzoj4756 [Usaco2017 Jan]Promotion Counting

传送门：http://www.lydsy.com/JudgeOnline/problem.php?id=4756

【题解】

dsu on tree，树状数组直接上

O(nlog^2n)

# include <vector>
# include <stdio.h>
# include <string.h>
# include <iostream>
# include <algorithm>
// # include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
const int M = 2e5 + , N = 4e5 + ;
const int mod = 1e9+;

# define RG register
# define ST static

int n, a[M];
vector<int> ps;
int ans[M];

int head[M], nxt[M], to[M], tot=;
inline void add(int u, int v) {
    ++tot; nxt[tot] = head[u]; head[u] = tot; to[tot] = v;
}

# define lb(x) (x&(-x))
struct BIT {
    int c[N];
    inline void edt(int x, int d) {
        for (; x<=n; x+=lb(x)) c[x] += d;
    }
    inline int sum(int x) {
        int ret = ;
        for (; x; x-=lb(x)) ret += c[x];
        return ret;
    }
    inline int sum(int x, int y) {
        if(x>y) return ;
        return sum(y) - sum(x-);
    }
}T;
# undef lb

int sz[M];
inline void dfssize(int x) {
    sz[x] = ;
    for (int i=head[x]; i; i=nxt[i]) {
        dfssize(to[i]);
        sz[x] += sz[to[i]];
    }
}

bool big[M];
inline void dfsans(int x) {
    T.edt(a[x], );
    for (int i=head[x]; i; i=nxt[i])
        if(!big[to[i]]) dfsans(to[i]);
}

inline void delans(int x) {
    T.edt(a[x], -);
    for (int i=head[x]; i; i=nxt[i])
        if(!big[to[i]]) delans(to[i]);
}

inline void dsu(int x, bool iskep) {
    int mx = -, bigc = -;
    for (int i=head[x]; i; i=nxt[i])
        if(sz[to[i]] > mx) mx = sz[to[i]], bigc = to[i];
    for (int i=head[x]; i; i=nxt[i])
        if(to[i] != bigc) dsu(to[i], );
    if(bigc != -) big[bigc] = , dsu(bigc, );
    dfsans(x);
    ans[x] = T.sum(a[x]+, n);
    if(bigc != -) big[bigc] = ;
    if(!iskep) delans(x);
}

int main() {
    cin >> n;
    for (int i=; i<=n; ++i) {
        scanf("%d", &a[i]);
        ps.push_back(a[i]);
    }

    sort(ps.begin(), ps.end());
    ps.erase(unique(ps.begin(), ps.end()), ps.end());

    for (int i=; i<=n; ++i) a[i] = lower_bound(ps.begin(), ps.end(), a[i]) - ps.begin() + ;

    for (int i=, fa; i<=n; ++i) {
        scanf("%d", &fa);
        add(fa, i);
    }

    dfssize();
    dsu(, );

    for (int i=; i<=n; ++i) printf("%d\n", ans[i]);

    return ;
}