Submission #1026122

#	Time	Username	Problem	Language	Result	Execution time	Memory
1026122		Muhammet	Torrent (COI16_torrent)	C++17	100 / 100	244 ms	27004 KiB

torrent

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

#define ll long long int
#define sz(x) (int)x.size()
#define ff first
#define ss second

const ll N = 300005;
const ll M = 1e9 + 7;

int T, n, a, b, c, d, p[N];

bool tr = 0, tr1 = 0;

vector <int> v[N], v1;

void dfs1(int x){
	if(x == 0) return;
	v1.push_back(x);
	dfs1(p[x]);
}

void dfs(int x, int y){
	p[x] = y;
	for(auto i : v[x]){
		if(i != y) {
			dfs(i,x);
		}
	}
}

int df(int x, int y){
	vector <int> v2;
	for(auto i : v[x]){
		if((i != y) and (min(x,i) != min(c,d) or max(x,i) != max(c,d))){
			v2.push_back(df(i,x));
		}
	}
	sort(v2.rbegin(), v2.rend());
	int mx = 0;
	for(int i = 0; i < sz(v2); i++){
		mx = max(mx, v2[i] + i + 1);
	}
	return mx;
}

int main(){
	ios::sync_with_stdio(false); cin.tie(0);

	cin >> n >> a >> b;

	for(int i = 1; i < n; i++){
		int x, y;
		cin >> x >> y;
		v[x].push_back(y);
		v[y].push_back(x);
	}

	dfs(a,0);

	dfs1(b);

	reverse(v1.begin(), v1.end());

	int l = 0, r = sz(v1)-2, k = 0;
	while(l <= r){
		int md = (l + r) / 2;
		c = v1[md], d = v1[md+1];
		if(df(a,0) < df(b,0)){
			l = md+1;
			k = md;
		}
		else {
			r = md-1;
		}
	}

	c = v1[k], d = v1[k+1];
	int mn = max(df(a,0),df(b,0));
	if(sz(v1) > 1){
		c = v1[k+1], d = v1[k+2];
		mn = min(mn,max(df(a,0),df(b,0)));
	}
	if(sz(v1) > 2){
		c = v1[k+2], d = v1[k+3];
		mn = min(mn,max(df(a,0),df(b,0)));
	}

	cout << mn;

	return 0;
}

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