Codeforces Round #316 (Div. 2) D. Tree Requests

鏈接

https://codeforces.com/contest/570/problem/D

題解

$dsu\ on\ tree$
對於每個深度統計每種字符的數目，如果數目爲奇數的字符不多於$1$種就能構成迴文

代碼

#include <bits/stdc++.h>
#define maxn 500010
#define maxe 1000010
using namespace std;
struct Graph
{
    int etot, head[maxn], to[maxe], next[maxe], w[maxe];
    void clear(int N)
    {
        for(int i=1;i<=N;i++)head[i]=0;
        etot=0;
    }
    void adde(int a, int b, int c){to[++etot]=b;w[etot]=c;next[etot]=head[a];head[a]=etot;}
}G;
struct ShuLianPouFen
{
    int size[maxn], top[maxn], tid[maxn], tim, untid[maxn], deep[maxn], son[maxn], fa[maxn];
    void dfs1(Graph &G, int pos)
    {
        int p, v;
        size[pos]=1;
        for(p=G.head[pos];p;p=G.next[p])
        {
            if((v=G.to[p])==fa[pos])continue;
            fa[v]=pos;
            deep[v]=deep[pos]+1;
            dfs1(G,v);
            if(size[v]>size[son[pos]])son[pos]=v;
            size[pos]+=size[v];
        }
    }
    void dfs2(Graph &G, int pos, int tp)
    {
        int p, v;
        top[pos]=tp;
        tid[pos]=++tim;
        untid[tid[pos]]=pos;
        if(son[pos])dfs2(G,son[pos],tp);
        for(p=G.head[pos];p;p=G.next[p])
            if((v=G.to[p])!=fa[pos] and v!=son[pos])dfs2(G,v,v);
    }
    void run(Graph &G, int root)
    {
        tim=0;
        deep[root]=1;
        dfs1(G,root);
        dfs2(G,root,root);
    }
}SP;
int ans[maxn], N, M, h[maxn], cnt[maxn][30], c[maxn], forb;
char s[maxn];
vector<int> qlis[maxn];
void force(int pos, int pre, int opt)
{
    cnt[SP.deep[pos]][c[pos]]+=opt;
    for(auto p=G.head[pos];p;p=G.next[p])
        if(G.to[p]!=pre and G.to[p]!=forb)
            force(G.to[p],pos,opt);
}
void dfs(int pos, int pre, int H)
{
    for(auto p=G.head[pos];p;p=G.next[p])
        if(G.to[p]!=pre and G.to[p]!=SP.son[pos])
            dfs(G.to[p],pos,0);
    if(SP.son[pos])dfs(SP.son[pos],pos,1);
    forb=SP.son[pos];
    force(pos,pre,+1);
    for(auto q:qlis[pos])
    {
        int x=0;
        for(int i=1;i<=26;i++)x+=(cnt[h[q]][i])&1;
        if(x<=1)ans[q]=true;
    }
    forb=0;
    if(H==0)force(pos,pre,-1);
}
int main()
{
    int i, j, p;
    ios::sync_with_stdio(false);
    cin>>N>>M;
    for(i=2;i<=N;i++)
    {
        cin>>p;
        G.adde(p,i,0);
        G.adde(i,p,0);
    }
    SP.run(G,1);
    cin>>s+1;
    for(i=1;i<=N;i++)c[i]=s[i]-'a'+1;
    for(i=1;i<=M;i++)
    {
        int v;
        cin>>v>>h[i];
        qlis[v].emplace_back(i);
    }
    dfs(1,0,0);
    for(i=1;i<=M;i++)
        if(ans[i])cout<<"Yes\n";
        else cout<<"No\n";
    return 0;
}