Solution -「BZOJ #3786」星系探索

$\mathcal{Description}$

  Link.

  给定一棵含 $n$ 个点的有根树，点有点权，支持 $q$ 次操作：

1. 询问 $u$ 到根的点权和；
2. 修改 $u$ 的父亲，保证得到的图仍是树；
3. 将 $u$ 子树内的点权增加一常数。

  $n\le10^5$，$q\le3\times10^5$。

$\mathcal{Solution}$

  ETT (Euler Tour Tree)，是一种能快速处理子树移动的动态树。本质上，它将树保存作欧拉序，由于子树移动体现在欧拉序上是区间移动，那么就能使用平衡树维护序列。路径查询亦对应了一段区间内仅出现一次的结点贡献和，记每个结点第一次出现为正贡献，后一次出现为负贡献就变成了区间查询，亦能用平衡树维护。本题即 ETT 板题。

  复杂度自然是 $\mathcal O((n+q)\log n)$ 的。

$\mathcal{Code}$

/*~Rainybunny~*/

#include <cstdio>
#include <cassert>
#include <cstdlib>

#define rep( i, l, r ) for ( int i = l, rep##i = r; i <= rep##i; ++i )
#define per( i, r, l ) for ( int i = r, per##i = l; i >= per##i; --i )

typedef long long LL;

const int MAXN = 1e5;
int n, ecnt, head[MAXN + 5], w[MAXN + 5], root, st[MAXN + 5], ed[MAXN + 5];
struct Edge { int to, nxt; } graph[MAXN + 5];

inline void link( const int s, const int t ) {
    graph[++ecnt] = { t, head[s] }, head[s] = ecnt;
}

struct Treap {
    static const int MAXND = MAXN << 1;
    int node, ch[MAXND + 5][2], fa[MAXND + 5], siz[MAXND + 5], aux[MAXND + 5],
      sign[MAXND + 5], ssiz[MAXND + 5];
    LL val[MAXND + 5], sum[MAXND + 5], tag[MAXND + 5];

    Treap() { srand( 20120712 ); }

    inline int crtnd( const int v, const int s ) {
        int u = ++node;
        aux[u] = rand(), siz[u] = 1;
        sign[u] = ssiz[u] = s;
        val[u] = sum[u] = v * s;
        return u;
    }

    inline void pushad( const int u, const LL x ) {
        val[u] += sign[u] * x, tag[u] += x, sum[u] += x * ssiz[u];
    }

    inline void pushup( const int u ) {
        siz[u] = siz[ch[u][0]] + siz[ch[u][1]] + 1;
        ssiz[u] = ssiz[ch[u][0]] + ssiz[ch[u][1]] + sign[u];
        sum[u] = sum[ch[u][0]] + sum[ch[u][1]] + val[u];
    }

    inline void pushdn( const int u ) {
        if ( tag[u] ) {
            if ( ch[u][0] ) pushad( ch[u][0], tag[u] );
            if ( ch[u][1] ) pushad( ch[u][1], tag[u] );
            tag[u] = 0;
        }
    }

    inline int merge( const int u, const int v ) {
        if ( !u || !v ) return u | v;
        pushdn( u ), pushdn( v );
        if ( aux[u] < aux[v] ) {
            ch[u][1] = merge( ch[u][1], v );
            if ( ch[u][1] ) fa[ch[u][1]] = u;
            return pushup( u ), u;
        } else {
            ch[v][0] = merge( u, ch[v][0] );
            if ( ch[v][0] ) fa[ch[v][0]] = v;
            return pushup( v ), v;
        }
    }

    inline void rsplit( const int u, const int k, int& x, int& y ) {
        if ( !u ) return void( x = y = 0 );
        fa[u] = 0, pushdn( u );
        if ( siz[ch[u][0]] >= k ) {
            y = u, rsplit( ch[u][0], k, x, ch[y][0] );
            if ( ch[y][0] ) fa[ch[y][0]] = y;
        } else {
            x = u, rsplit( ch[u][1], k - siz[ch[u][0]] - 1, ch[x][1], y );
            if ( ch[x][1] ) fa[ch[x][1]] = x;
        }
        pushup( u );
    }

    inline int rank( int u ) {
        int ret = siz[ch[u][0]] + 1;
        while ( fa[u] ) {
            if ( ch[fa[u]][1] == u ) ret += siz[ch[fa[u]][0]] + 1;
            u = fa[u];
        }
        return ret;
    }
} trp;

inline void init( const int u ) {
    root = trp.merge( root, st[u] = trp.crtnd( w[u], 1 ) );
    for ( int i = head[u]; i; i = graph[i].nxt ) init( graph[i].to );
    root = trp.merge( root, ed[u] = trp.crtnd( w[u], -1 ) );
}

inline LL query( const int u ) {
    int l = trp.rank( st[1] ), r = trp.rank( st[u] ), x, y, z;
    assert( l == 1 );
    trp.rsplit( root, l - 1, x, y ), trp.rsplit( y, r - l + 1, y, z );
    LL ret = trp.sum[y];
    root = trp.merge( x, trp.merge( y, z ) );
    return ret;
}

inline void change( const int u, const int p ) {
    int l = trp.rank( st[u] ), r = trp.rank( ed[u] ), tar = trp.rank( st[p] ),
      x, y, z, m;
    if ( tar < l ) {
        trp.rsplit( root, tar, x, y );
        trp.rsplit( y, l - tar - 1, y, z );
        trp.rsplit( z, r - l + 1, z, m );
    } else {
        trp.rsplit( root, l - 1, x, y );
        trp.rsplit( y, r - l + 1, y, z );
        trp.rsplit( z, tar - r, z, m );
    }
    root = trp.merge( trp.merge( x, z ), trp.merge( y, m ) );
}

inline void update( const int u, const int p ) {
    int l = trp.rank( st[u] ), r = trp.rank( ed[u] ), x, y, z;
    trp.rsplit( root, l - 1, x, y ), trp.rsplit( y, r - l + 1, y, z );
    trp.pushad( y, p ), root = trp.merge( x, trp.merge( y, z ) );
}

int main() {
    scanf( "%d", &n );
    for ( int i = 2, t; i <= n; ++i ) scanf( "%d", &t ), link( t, i );
    rep ( i, 1, n ) scanf( "%d", &w[i] );

    init( 1 );

    char op[5]; int q, a, b;
    for ( scanf( "%d", &q ); q--; ) {
        scanf( "%s %d", op, &a );
        if ( op[0] == 'Q' ) printf( "%lld\n", query( a ) );
        else if ( op[0] == 'C' ) scanf( "%d", &b ), change( a, b );
        else scanf( "%d", &b ), update( a, b );
    }
    return 0;
}