Submission #223645

#	Time	Username	Problem	Language	Result	Execution time	Memory
223645		MohamedAhmed04	Torrent (COI16_torrent)	C++14	100 / 100	567 ms	28232 KiB

torrent

#include <bits/stdc++.h>

using namespace std ;

const int MAX = 3e5 + 10 ;

int dep[MAX] , P[MAX] , sz[MAX] ;
int n , a , b ;

vector< vector<int> >adj(MAX) ;

void dfs1(int node , int par)
{
	P[node] = par ;
	for(auto &child : adj[node])
	{
		if(child == par)
			continue ;
		dep[child] = dep[node] + 1 ;
		dfs1(child , node) ;
	}
	return ;
}

int x , y ;

int dfs2(int node , int par)
{
	vector<int>v ;
	for(auto &child : adj[node])
	{
		if(child == par)
			continue ;
		if((child == x && y == node) || (child == y && node == x))
			continue ;
		v.push_back(dfs2(child , node)) ;
	}
	sort(v.rbegin() , v.rend()) ;
	int cnt = 0 ;
	for(int i = 0 ; i < v.size() ; ++i)
		cnt = max(cnt , v[i]+1+i) ;
	return cnt ;
}

int check(int mid , bool flag)
{
	int now = b ;
	while(dep[now] != mid)
		now = P[now] ;
	x = P[now] , y = now ;
	if(!flag)
		return (dfs2(a,-1) <= dfs2(b,-1)) ;
	else
		return max(dfs2(a , -1) , dfs2(b , -1)) ;
}

int main()
{
	ios_base::sync_with_stdio(0) ;
	cin.tie(0) ;
	cin>>n>>a>>b ;
	for(int i = 0 ; i < n-1 ; ++i)
	{
		int x , y ;
		cin>>x>>y ;
		adj[x].push_back(y) ;
		adj[y].push_back(x) ;
	}
	dfs1(a , -1) ;
	int l = 1 , r = dep[b] ;
	int ans = 0 ;
	while(l <= r)
	{
		int mid = (l + r) >> 1 ;
		if(check(mid , 0))
			ans = mid , l = mid+1 ;
		else
			r = mid-1 ;
	}
	//cout<<ans<<" : "<<check(ans , 1)<<"\n" ;
	int ans2 = check(ans , 1) ;
	if(ans-1 > 0)
		ans2 = min(ans2 , check(ans-1 , 1)) ;
	if(ans+1 <= dep[b])
		ans2 = min(ans2 , check(ans+1 , 1)) ;
	return cout<<ans2<<"\n" , 0 ;
}		

Compilation message (stderr)

torrent.cpp: In function 'int dfs2(int, int)':
torrent.cpp:40:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0 ; i < v.size() ; ++i)
                  ~~^~~~~~~~~~

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