結果

問題 No.778 クリスマスツリー
コンテスト
ユーザー fumiphys
提出日時 2020-02-28 21:52:12
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 125 ms / 2,000 ms
コード長 5,201 bytes
コンパイル時間 1,926 ms
コンパイル使用メモリ 180,372 KB
実行使用メモリ 28,284 KB
最終ジャッジ日時 2024-10-14 02:01:39
合計ジャッジ時間 3,468 ms
ジャッジサーバーID
（参考情報） 		judge4 / judge3
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 3
other AC * 12
権限があれば一括ダウンロードができます

ソースコード

diff # 

// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL<<(n))
// functions
template <typename T> void unique(T& c){c.erase(std::unique(c.begin(), c.end()), c.end());}
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << "(" << p.first << ", " << p.second << ")"; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(nullptr); cout << fixed << setprecision(20);}
} fast_io_;

template <class Monoid>
class SegmentTree{
  public:
    int n;
    using T = typename Monoid::value_type;
    vector<T> val;
    T identity;

    SegmentTree(){}
    SegmentTree(int n_, vector<T> v=vector<T>()){
      n = 1;
      while(n < n_)n *= 2;
      identity = Monoid::identity;
      val.assign(2*n-1, identity);

      for(size_t i = 0; i < v.size(); i++){
        val[i+n-1] = v[i];
      }
      for(int i = n - 2; i >= 0; i--){
        val[i] = Monoid::operation(val[2*i+1], val[2*i+2]);
      }
    }
    void update(int k, const T &t){
      k = k + n - 1;
      val[k] = t;
      while(k > 0){
        k = (k - 1) / 2;
        val[k] = Monoid::operation(val[2*k+1], val[2*k+2]);
      }
    }
    T query(int a, int b, int k, int l, int r){
      if(r <= a || b <= l)return identity;
      if(a <= l && r <= b)return val[k];
      T lv = query(a, b, 2*k+1, l, (l+r)/2);
      T rv = query(a, b, 2*k+2, (l+r)/2, r);
      return Monoid::operation(lv, rv);
    }
    T query(int a, int b){
      return query(a, b, 0, 0, n);
    }
    T get(int i){
      return val[i+n-1];
    }
};

template <typename T>
class RSQ{
  public:
    const static T identity = 0;
    using value_type = T;

    RSQ(){}
    static T operation(T &l, T &r){
      return l + r;
    }
};


class EulerTourTree{
  public:
    int n;
    vector<vector<int>> edges;
    // [b, e)
    vector<int> b, e;
    vector<int> v;
    EulerTourTree(){}
    EulerTourTree(int n): n(n){
      edges.resize(n);
    }
    void adde(int from, int to){
      edges[from].emplace_back(to);
    }
    void dfs(int i, int par){
      b[i] = int(v.size());
      v.emplace_back(i);
      for(auto e: edges[i]){
        if(e == par)continue;
        dfs(e, i);
      }
      e[i] = int(v.size());
    }
    void build(int r = 0){
      b.resize(n, -1);
      e.resize(n, -1);
      v.reserve(n);
      v.resize(0);
      dfs(r, -1);
    }
};

int main(int argc, char const* argv[])
{
  int n; cin >> n;
  EulerTourTree ett(n);
  rep(i, n - 1){
    int a; cin >> a;
    ett.adde(a, i + 1);
  }
  ett.build();
  ll res = 0;
  SegmentTree<RSQ<ll>> seg(n);
  rrep(i, n){
    res += seg.query(ett.b[i], ett.e[i]);
    seg.update(ett.b[i], 1);
  }
  cout << res << endl;
  return 0;
}
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