Submission #1155835

#	Time	Username	Problem	Language	Result	Execution time	Memory
1155835		Ludissey	Cat in a tree (BOI17_catinatree)	C++20	0 / 100	1 ms	324 KiB

catinatree

#include <bits/stdc++.h>
#define int long long
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
 
using namespace std;

int n,d;
vector<vector<int>> neigh;
vector<int> cindex;
vector<int> memo;
vector<int> dist;
vector<int> childC;
int mxC=0;


int build_tree(int x, int p){
    childC[x]=1;
    for (int t=0; t<sz(neigh[x]); t++)
    {
        int u=neigh[x][t];
        if(u==p||cindex[u]>=0) continue;
        childC[x]+=build_tree(u,x);
    }
    return childC[x];
}

int centroid(int x, int p, int _n){
    for (int t=0; t<sz(neigh[x]); t++)
    {
        int u=neigh[x][t];
        if(u==p||cindex[u]>=0) continue;
        if(childC[u]*2>=_n) return centroid(u,x,_n);
    }
    return x;
}

void decompo(int x, int compoINDEX){
    build_tree(x,-1);
    if(childC[x]==1) { cindex[x]=compoINDEX; mxC=max(compoINDEX,mxC); return;}
    int c=centroid(x,-1,childC[x]);
    cindex[c]=compoINDEX;
    mxC=max(compoINDEX,mxC);
    for (auto u : neigh[c])
    {
        if(cindex[u]>=0) continue;
        decompo(u,compoINDEX+1);
    }
}
int calc(int x, int p, int dst, int indx){
    dist[min(d,dst)]=max(dist[min(d,dst)],memo[x]);
    int mx=dst;
    for (auto u : neigh[x])
    {
        if(u==p||cindex[u]<=indx) continue;
        mx=max(mx,calc(u,x,dst+1,indx));
    }
    return mx;
}

int dp(int x){
    if(memo[x]!=-1) return memo[x];
    vector<vector<int>> clc(sz(neigh[x]));
    int mxS=0;
    for (int t=0; t<sz(neigh[x]); t++)
    {
        int u=neigh[x][t];
        if(cindex[u]<=cindex[x]) continue;
        mxS=max(calc(u,x,1,cindex[x]),mxS);
        clc[t].resize(1);
        clc[t][0]=0;
        for (int i = 1; i <= d; i++)
        {
            if(dist[i]==-1) break;
            clc[t][i]=dist[i];
            dist[i]=-1;
        }
    }
    mxS++;
    vector<pair<int,int>> mxdist(mxS,{-1,-1});
    mxdist[0]={0,0};
    for (int t=0; t<sz(neigh[x]); t++)
    {
        int u=neigh[x][t];
        if(cindex[u]<=cindex[x]) continue;
        for (int i = 0; i < sz(clc); i++)
        {
            if(clc[t][i]>mxdist[i].first) { mxdist[i].second=mxdist[i].first; mxdist[i].first=clc[t][i]; }
            else if(clc[t][i]>mxdist[i].second) mxdist[i].second=clc[t][i];
        }
    }
    memo[x]=1;
    for (int t=0; t<sz(neigh[x]); t++)
    {
        int u=neigh[x][t];
        if(cindex[u]<=cindex[x]) continue;
        for (int i = 0; i < sz(clc); i++)
        {
            if(d-i>=sz(mxdist)) continue;
            int v=mxdist[d-i].first;
            if(d-i<=sz(clc)&&v==clc[t][d-i]) v=mxdist[d-i].second;
            memo[x]=max(memo[x],v+clc[t][i]+2);
        }
    }
    return memo[x];
}

signed main() {
    ios_base::sync_with_stdio(false); cin.tie(nullptr);
    cin >> n >> d;
    cindex.resize(n,-1); childC.resize(n); dist.resize(d+1,-1); neigh.resize(n); memo.resize(n,-1);
    for (int i = 1; i < n; i++)
    {
        int x; cin >> x;
        neigh[x].push_back(i);
        neigh[i].push_back(x);
    }
    decompo(0,0);
    mxC++;
    vector<vector<int>> grp(mxC);
    for (int i = 0; i < n; i++)
    {
        grp[cindex[i]].push_back(i);
    }
    int ans=0;
    for (int c = mxC-1; c >= 0; c--) {
        for (auto u : grp[c])
        {
            ans=max(ans,dp(u));
        }
    }
    cout << ans << "\n";
    return 0;
}

• Subtask 1: 0 / 11
• Subtask 2: 0 / 40
• Subtask 3: 0 / 49