Submission #1068658

#	Time	Username	Problem	Language	Result	Execution time	Memory
1068658		kunzaZa183	Torrent (COI16_torrent)	C++17	100 / 100	674 ms	53832 KiB

torrent

#include <bits/stdc++.h>
using namespace std;
int main() {
  //cin.tie(0)->sync_with_stdio(0);
  int n,st,ed;
  cin>>n>>st>>ed;
  st--,ed--;
  vector<set<int>> adjlist(n);
  for(int i = 0; i < n - 1;i++)
  {
    int x,y;
    cin>>x>>y;
    x--,y--;
    adjlist[x].insert(y),adjlist[y].insert(x);
  }
    
  vector<int> bet(n);
  vector<int> path;

  function<void(int,int)> fp = [&](int cur,int par) {
    path.push_back(cur);
    if(cur==ed){
      return;
    }
    for(auto a:adjlist[cur])
      if(a!=par) {
        fp(a,cur);
        if(path.back()==ed)
          return;
      }
    path.pop_back();
  };
  fp(st,st);

  function<int(int,int)> dfs = [&](int cur,int par) {
    vector<int> vi;
    for(auto a:adjlist[cur])
      if(a!=par)
        vi.push_back(dfs(a, cur));
    sort(vi.begin(),vi.end(),greater<int>());
    for(int i = 0; i < vi.size();i++)
      vi[i] += i+1;
    if(vi.empty())
      return 0;
    return *max_element(vi.begin(),vi.end());
  };


  int maxans = n;
  int l =0 , r = path.size() - 2;
  while(l<=r) {
    int mid = (l+r)/2;
    int x = path[mid], y = path[mid + 1];
    adjlist[x].erase(y),adjlist[y].erase(x);
    int a1 = dfs(st,st), a2 = dfs(ed,ed);
    maxans = min(maxans, max(a1,a2));
    if(a1>a2)
      r = mid-1;
    else if(a1 <= a2)
      l= mid + 1;
    adjlist[x].insert(y),adjlist[y].insert(x);
  }
  cout<<maxans<<"\n";
}

Compilation message (stderr)

torrent.cpp: In lambda function:
torrent.cpp:41:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   41 |     for(int i = 0; i < vi.size();i++)
      |                    ~~^~~~~~~~~~~

• Subtask 1: 31 / 31
• Subtask 2: 69 / 69