Submission #127877

#	Time	Username	Problem	Language	Result	Execution time	Memory
127877		Adhyyan1252	Torrent (COI16_torrent)	C++11	100 / 100	446 ms	28040 KiB

torrent

#include<bits/stdc++.h>
#define DEBUG false
using namespace std;

int n, a, b; 

vector<vector<int> > g;
vector<int> s;
vector<int> c;
bool dfs(int cur, int par){
	s.push_back(cur);
	if(cur == b){
		return true;
	}
	for(int u: g[cur]){
		if(u == par) continue;
		if(dfs(u, cur)) return true;
	}
	s.pop_back();
	return false;
}

int dfs2(int cur, int par){
	vector<int> f;
	for(int u: g[cur]){
		if(c[u] || u == par) continue;
		f.push_back(dfs2(u, cur));
	}
	sort(f.rbegin(), f.rend());
	int ans = 0;
	for(int i = 0; i < f.size(); i++){
		ans = max(ans, f[i] + i+1);
	}
	return ans;
}

vector<vector<int> > h;


bool sim(int v){
	if(DEBUG) cout<<"SIM "<<v<<endl;
	int l1 = 0, l2 = 0;
	int r1 = h.size()-1, r2 = 0;
	bool pos = true;
	int tym = 0;
	while(l1 < r1){
		if(l2 == h[l1].size() || h[l1][l2] + tym - (l2) + 1 <= v){
			l1++; l2 = 0;
		}else{
			if(h[l1][l2] + tym - l2 > v){
				return false;
			}
			l2++;
		}
		
		
		if(r2 == h[r1].size() || h[r1][r2] + tym - (r2) + 1 <= v){
			r1--; r2 = 0;
		}else{
			if(h[r1][r2] + tym - r2 > v){
				return false;
			}
			r2++;
		}
		tym++;
	}
	if(l2 == h[l1].size()) l1++;
	if(r2 == h[r1].size()) r1--;
	if(l1 == r1){
		if(h[l1][max(l2, r2)] + tym - max(l2, r2) > v) return false;
	}
	return tym <= v;
}


signed main(){
	cin>>n>>a>>b; a--, b--;
	g.resize(n);
	c.resize(n);
	for(int i = 0; i < n-1; i++){
		int x, y; cin>>x>>y; x--, y--;
		g[x].push_back(y);
		g[y].push_back(x);
	}
	
	dfs(a, -1);
	for(int u: s){
		c[u] = 1;
	}
	if(DEBUG)
	for(int u: s){
		cout<<" S: "<<u<<endl;
	}
	
	for(int u: s){
		if(DEBUG) cout<<"DOING "<<u<<endl;
		vector<int> k;
		for(int d: g[u]){
			if(c[d]) continue;
			if(DEBUG) cout<<"DFS2 "<<d<<" "<<u<<endl;
			k.push_back(dfs2(d, u));
		}
		sort(k.rbegin(), k.rend());
		for(int i = 0; i < k.size(); i++) k[i] += i+1;
		for(int i = k.size()-2; i >= 0; i--){
			k[i] = max(k[i], k[i+1]);
		}
		h.push_back(k);
	}
	if(DEBUG)
	for(vector<int> k: h){
		for(int u: k){
			cout<<u<<" ";
		}
		cout<<endl;
	}
	
	
//	cout<<"SIM 2: "<<sim(2)<<endl;
	int low = 0, high = n, mid;
	while(low < high){
		mid = (low + high)/2;
		
		//run it with ans mid and check if its possible
		
		bool pos = sim(mid);
		
		if(pos){
			high = mid;
		}else{
			low = mid+1;
		}
	}
	mid = (low + high)/2;
	cout<<mid<<endl;
}

Compilation message (stderr)

torrent.cpp: In function 'int dfs2(int, int)':
torrent.cpp:31:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < f.size(); i++){
                 ~~^~~~~~~~~~
torrent.cpp: In function 'bool sim(int)':
torrent.cpp:47:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(l2 == h[l1].size() || h[l1][l2] + tym - (l2) + 1 <= v){
      ~~~^~~~~~~~~~~~~~~
torrent.cpp:57:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(r2 == h[r1].size() || h[r1][r2] + tym - (r2) + 1 <= v){
      ~~~^~~~~~~~~~~~~~~
torrent.cpp:67:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(l2 == h[l1].size()) l1++;
     ~~~^~~~~~~~~~~~~~~
torrent.cpp:68:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(r2 == h[r1].size()) r1--;
     ~~~^~~~~~~~~~~~~~~
torrent.cpp:44:7: warning: unused variable 'pos' [-Wunused-variable]
  bool pos = true;
       ^~~
torrent.cpp: In function 'int main()':
torrent.cpp:104:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < k.size(); i++) k[i] += i+1;
                  ~~^~~~~~~~~~

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