Submission #855900

#	Time	Username	Problem	Language	Result	Execution time	Memory
855900		mychecksedad	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	605 ms	75336 KiB

mousetrap

/* Author : Mychecksdead  */
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define MOD (1000000000+7)
#define MOD1 (998244353)
#define pb push_back
#define all(x) x.begin(), x.end()
#define en cout << '\n'
const int N = 1e6+100, M = 1e5+10, K = 22;

struct Fenwick{
  int n;
  vector<int> t;
  Fenwick(int _n){
    n = _n;
    t.resize(n+1, 0);
  }
  void add(int v, int x){
    while(v <= n){
      t[v] += x;
      v += (v&-v);
    }
  }
  int get(int v){
    int res = 0;
    while(v > 0){
      res += t[v];
      v -= (v&-v);
    }
    return res;
  }
};
 

int n, s, t, dp[N], pd[N], ch[N];
ll ans = 0;
vector<int> g[N], P;

bool dfs(int v, int p){
  if(v == t) return 1;
  bool ok = 0;
  dp[v] = 0;
  pd[v] = 0;
  vector<int> dps;
  int child_t = -1;
  for(int u: g[v]){
    if(u != p){
      bool b = dfs(u, v);
      if(!b)
        dps.pb(dp[u] + 1);
      if(b)
        child_t = u;
      ok |= b;
    }
  }
  ch[v] = child_t;
  sort(all(dps), greater<int>());
  if(ok){
    pd[v] = pd[child_t] + int(dps.size());
  }else{
    dp[v] = dps.size() <= 1 ? int(dps.size()) : dps[1] + (dps.size() - 1);
  }
  // cout << dp[v] << ' ' << v << ' ' << pd[v] << '\n';
  if(ok) P.pb(v);
  return ok;
}

void solve(){
  cin >> n >> t >> s;
  for(int i = 0; i < n - 1; ++i){
    int u, v; cin >> u >> v;
    g[u].pb(v);
    g[v].pb(u);
  }
  dp[t] = pd[t] = 0;
  dfs(s, 0);
  int ans = MOD;
  vector<pair<int, int>> A;
  int sz = P.size();
  Fenwick fw(sz);
  reverse(all(P));
  for(int i = 0; i < sz; ++i){
    int v = P[i];
    fw.add(i + 1, 1);
    for(int u: g[v]){
      if(ch[u] != v && u != ch[v]){
        A.pb({pd[v] + dp[u], i});
        // cout << u << ' ' << v << '\n';
      }
    }
    // cout << P[i] << endl;
  }
  // en;
  sort(all(A), greater<pair<int, int>>());

  for(int i = 0; i < A.size(); ++i){
    // cout << A[i].first << ' ' << A[i].second << '\n';
    int pos = A[i].second;
    if(fw.get(pos + 1) > 0){
      fw.add(pos + 1, -1);
    }else ans = min(ans, A[i].first + pos - fw.get(pos));
  }


  cout << (ans==MOD?int(A.size()):ans);
}


int main(){
  cin.tie(0); ios::sync_with_stdio(0);
  int tt = 1, aa;
  // freopen("in.txt", "r", stdin);
  // freopen("out.txt", "w", stdout);
  while(tt--){
    solve();
  }
  cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" seconds\n";
  return 0;
} 

Compilation message (stderr)

mousetrap.cpp: In function 'void solve()':
mousetrap.cpp:97:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   97 |   for(int i = 0; i < A.size(); ++i){
      |                  ~~^~~~~~~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:112:15: warning: unused variable 'aa' [-Wunused-variable]
  112 |   int tt = 1, aa;
      |               ^~

• Subtask 1: 0 / 20
• Subtask 2: 0 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35