Submission #704686

#	Time	Username	Problem	Language	Result	Execution time	Memory
704686		Ronin13	Cat in a tree (BOI17_catinatree)	C++14	100 / 100	590 ms	67352 KiB

catinatree

#include <bits/stdc++.h>
#define ll long  long
#define f first
#define s second
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define epb emplace_back

using namespace std;
const int nmax = 2e5 + 1;
vector <vector <pii> > cent(nmax);

vector <bool> marked(nmax);
vector <int> sz(nmax);
vector <int> mx(nmax);
vector <vector <int> > g(nmax);
vector <int> cur(nmax, 1e9);

void dfs(int v, int e = -1){
    sz[v] = 1;
    mx[v] = 0;
    for(int to : g[v]){
        if(marked[to]) continue;
        if(to == e) continue;
        dfs(to, v);
        sz[v] += sz[to];
        mx[v] = max(mx[v], sz[to]);
    }
}

int find_cen(int v, int s, int e = -1){
    if(mx[v] <= s / 2){
        if(sz[v] >= s / 2) return v;
    }
    for(int to : g[v]){
        if(to == e || marked[to]) continue;
       int x  = find_cen(to, s, v);
       if(x != -1) return x;
    }
    return -1;
}

void DFS(int v, int d, int st,  int e = -1){
    cent[v].pb({d, st});
    for(int to : g[v]){
        if(to == e || marked[to]) continue;
        DFS(to, d + 1, st, v);
    }
}

void rec(int v){
    dfs(v);
    int x = find_cen(v, sz[v]);
    DFS(x, 0, x);
    marked[x] = true;
    for(int to : g[x]){
        if(!marked[to])
            rec(to);
    }
}

int getmn(int v){
    int ans = 1e9;
    for(auto cc : cent[v]){
        int x = cc.s, y = cc.f;
        ans = min(ans, cur[x] + y);
    }
    return ans;
}

void mark(int v){
    for(auto cc : cent[v]){
        int x = cc.s, y = cc.f;
        cur[x] = min(cur[x], y);
    }
}

vector <pii> vv;

void stupidguy(int v, int d, int e = -1){
    vv.pb({d, v});
    for(int to : g[v]){
        if(to == e) continue;
        stupidguy(to, d + 1, v);
    }
}

int main(){
    ios_base::sync_with_stdio(false); cin.tie(0);
    int n; cin >> n;
    int D; cin >> D;
    for(int i = 1; i < n; i++){
        int x; cin >> x;
        g[x].pb(i);
        g[i].pb(x);
    }
    rec(1);

    int ans = 0;
    stupidguy(1, 0);
    sort(vv.begin(), vv.end());
    for(int i = vv.size() - 1; i >= 0; i--){
        int x = vv[i].s;
        if(getmn(x) >= D){
            ans++;
            mark(x);
        }
    }
    cout << ans;
    return 0;
}

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*/

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