bzoj2815[灾难] 灭绝树 （ 灭绝树上灭绝果，灭绝树下你和我）

灭绝树的定义:

灭绝树上，如果 u 是 v 的父亲 ，如果 u 挂了，那么 v 也要挂 。

怎么构造灭绝树？

拓扑排序+lca

主要的思想：

一个点的前驱的LCA一定是一个数到根的必经点

作用：

找必经点

#include <queue>#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int N = 1e5 + 10 ;struct Edge {    int nxt , to ;};Edge e [ N * 20 ] , t [ N * 20 ] ;int head [N] , headt [N] ;int tot , tot1 , n ;int in [N] , fa [N] [25] , bin [20] , dep [N] , sz [N] ;vector <int> q , st ;void addeage ( int u , int v ) {    ++ tot ;    e [tot].nxt = head [u] ;    e [tot].to = v ;    head [u] = tot ;    in [v] ++ ;}void addeage1 ( int u , int v ) {    ++ tot1 ;    t [tot1].nxt = headt [u] ;    t [tot1].to = v ;    headt [u] = tot1 ;}void dfs ( int u ) {    sz [u] = 0 ;    for ( int i = headt [u] ; i ; i = t [i].nxt ) {        int v = t [i].to ;        if ( v == fa [u] [0] ) continue ;        fa [v] [0] = u ;        dfs ( v ) ;        sz [u] += sz [v] + 1 ;    }}void pre ( int u ) {    for ( int i = 1 ; bin [i] <= dep [u] ; ++ i ) {        fa [u] [i] = fa [ fa [u] [ i - 1 ] ] [ i - 1 ] ;    }}int LCA ( int u , int v ) {    if ( u == -1 ) return v ;    if ( dep [u] < dep [v] ) swap ( u , v ) ;    int t = dep [u] - dep [v] ;    for ( int i = 0 ; bin [i] <= t ; ++ i )        if ( t & bin [i] ) u = fa [u] [i] ;    if ( u == v ) return u ;    for ( int i = 17 ; i >= 0 ; -- i ) {        if ( fa [u] [i] != fa [v] [i] ) {            u = fa [u] [i] ;            v = fa [v] [i] ;        }    }    return fa [u] [0] ;}void top () {    for ( int i = 1 ; i <= n ; ++ i )         if ( ! in [i] ) st.push_back ( i ) ;    while ( ! st.empty () ) {        int u = st.back () ;        st.pop_back () ;        q.push_back ( u ) ;        for ( int i = head [u] ; i ; i = e [i].nxt ) {            int v = e [i].to ;            in [v] -- ;            if ( ! in [v] ) st.push_back ( v ) ;        }    }   }void build () {    for ( int i = q.size () - 1 ; i >= 0 ; -- i ) {        int u = q [i] ;        int fat = -1 ;        for ( int j = head [u] ; j ; j = e [j].nxt )             fat = LCA ( fat , e [j].to ) ;        if ( fat == -1 ) fat = 0 ;        addeage1 ( fat , u ) ;        dep [u] = dep [fat] + 1 ;        fa [u] [0] = fat ;        pre ( u ) ;    }}int main () {    bin [0] = 1 ;    for ( int i = 1 ; i < 20 ; ++ i ) bin [i] = bin [ i - 1 ] * 2 ;    scanf ( "%d" , & n ) ;    for ( int i = 1 ; i <= n ; ++ i ) {        int x ;        scanf ( "%d" , & x ) ;        while ( x != 0 ) {            addeage ( i , x ) ;            scanf ( "%d" , & x ) ;        }    }       top () ;    build () ;    dfs ( 0 ) ;    for ( int i = 1 ; i <= n ; ++ i )         printf ( "%d\n" , sz [i] ) ;    return 0 ;}