【LOJ】#2054. 「TJOI / HEOI2016」树

题解

一写过一交A的水题

只要求一个dfs序，新加一个标记在子树所在的区间上覆盖上该点，维护深度最大的答案

代码

#include <bits/stdc++.h>
#define enter putchar('
')
#define space putchar(' ')
#define pii pair<int,int>
#define fi first
#define se second
#define MAXN 100005
#define pb push_back
#define mp make_pair
#define eps 1e-8
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
template<class T>
void read(T &res) {
    res = 0;T f = 1;char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') f = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9') {
        res = res * 10 + c - '0';
        c = getchar();
    }
}
template<class T>
void out(T x) {
    if(x < 0) {x = -x;putchar('-');}
    if(x >= 10) out(x / 10);
    putchar('0' + x % 10);
}

int N,Q;
struct node {
    int to,next;
}E[MAXN * 2];

int head[MAXN],sumE,dfn[MAXN],idx,siz[MAXN],dep[MAXN];
namespace seg_tr {
    struct node {
        int l,r,cov;
    }tr[MAXN * 4];
    void build(int u,int l,int r) {
        tr[u].l = l;tr[u].r = r;
        if(l == r) {
            tr[u].cov = 1;
            return;
        }
        int mid = (l + r) >> 1;
        build(u << 1,l,mid);
        build(u << 1 | 1,mid + 1,r);
    }
    int max_dep(int a,int b) {
        return dep[a] < dep[b] ? b : a;
    }
    void cover(int u,int v) {
        if(!tr[u].cov) tr[u].cov = v;
        else tr[u].cov = max_dep(tr[u].cov,v);
    }
    void push_down(int u) {
        if(tr[u].cov) {
            cover(u << 1,tr[u].cov);
            cover(u << 1 | 1,tr[u].cov);
            tr[u].cov = 0;
        }
    }
    void Cover(int u,int l,int r,int v) {
        if(tr[u].l == l && tr[u].r == r) {cover(u,v);return;}
        int mid = (tr[u].l + tr[u].r) >> 1;
        push_down(u);
        if(r <= mid) Cover(u << 1,l,r,v);
        else if(l > mid) Cover(u << 1 | 1,l,r,v);
        else {Cover(u << 1,l,mid,v);Cover(u << 1 | 1,mid + 1,r,v);}
    }
    int Query(int u,int pos) {
        if(tr[u].l == tr[u].r) return tr[u].cov;
        push_down(u);
        int mid = (tr[u].l + tr[u].r) >> 1;
        if(pos <= mid) return Query(u << 1,pos);
        else return Query(u << 1 | 1,pos);
    }
}

void add(int u,int v) {
    E[++sumE].to = v;
    E[sumE].next = head[u];
    head[u] = sumE;
}
void dfs(int u,int fa) {
    dfn[u] = ++idx;
    siz[u] = 1;
    dep[u] = dep[fa] + 1;
    for(int i = head[u] ; i ; i = E[i].next) {
        int v = E[i].to;
        if(v != fa) {
            dfs(v,u);
            siz[u] += siz[v];
        }
    }
}
void Solve() {
    read(N);read(Q);
    int u,v;
    for(int i = 1 ; i < N ; ++i) {
        read(u);read(v);
        add(u,v);add(v,u);
    }
    dfs(1,0);
    seg_tr::build(1,1,N);
    char op[5];int a;
    while(Q--) {
        scanf("%s%d",op + 1,&a);
        if(op[1] == 'Q') {out(seg_tr::Query(1,dfn[a]));enter;}
        else {seg_tr::Cover(1,dfn[a],dfn[a] + siz[a] - 1,a);}
    }
}
int main() {
#ifdef ivorysi
    freopen("f1.in","r",stdin);
#endif
    Solve();
    return 0;
}