제출 #571526

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
571526		BackNoob	Torrent (COI16_torrent)	C++14	69 / 100	933 ms	34816 KiB

torrent

#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define endl '\n'
#define MASK(i) (1LL << (i))
#define ull unsigned long long
#define ld long double
#define pb push_back
#define all(x) (x).begin() , (x).end()
#define BIT(x , i) ((x >> (i)) & 1) 
#define TASK "task"
#define sz(s) (int) (s).size()

using namespace std;
const int mxN = 5e5 + 227;
const int inf = 1e9 + 277;
const int mod = 24211007;
const ll infll = 1e18 + 7;
const int base = 200;
const int LOG = 29;
 
template <typename T1, typename T2> bool minimize(T1 &a, T2 b) {
	if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b) {
	if (a < b) {a = b; return true;} return false;
}

int n;
int a, b;
vector<int> adj[mxN];
int par[mxN];
int dp1[mxN];
int dp2[mxN];
int res = inf;

void dfs(int u, int p)
{
	for(int v : adj[u]) {
		if(v == p) continue;
		par[v] = u;
		dfs(v, u);
	}
}

void calc_dp1(int u, int p, int x)
{
	vector<int> val;
	for(int v : adj[u]) {
		if(v == p || v == x) continue;
		calc_dp1(v, u, x);
		val.pb(dp1[v]);
	}
	sort(all(val));
	reverse(all(val));
	int cnt = 0;
	for(auto it : val) {
		++cnt;
		maximize(dp1[u], it + cnt);
	}
}

void calc_dp2(int u, int p, int x)
{
	vector<int> val;
	for(int v : adj[u]) {
		if(u == x && v == par[u]) continue;
		if(v == p) continue;
		calc_dp2(v, u, x);
		val.pb(dp2[v]);
	}
	sort(all(val));
	reverse(all(val));
	int cnt = 0;
	for(auto it : val) {
		++cnt;
		maximize(dp2[u], it + cnt);
	}
}



void calc(int x)
{
	for(int i = 1; i <= n; i++) dp1[i] = dp2[i] = 0;
	calc_dp1(a, -1, x);
	calc_dp2(b, -1, x);
	// cout << x << ' ' << dp1[a] << ' ' << dp2[b] << endl;
	minimize(res, max(dp1[a], dp2[b]));
}

void solve()
{	
	cin >> n >> a >> b;
	for(int i = 1; i < n; i++) {
		int u, v;
		cin >> u >> v;
		adj[u].pb(v);
		adj[v].pb(u);
	}

	dfs(a, -1);

	int x = b;
	vector<int> pos;
	while(x != a) {	
		pos.pb(x);
		x = par[x];
	}

	int lo = 1, hi = sz(pos);
	while(lo + 1 < hi) {
		int mid = (lo + hi) / 2;
		calc(pos[mid - 1]);
		if(dp1[a] > dp1[b]) lo = mid;
		else hi = mid;
	}

	calc(pos[lo - 1]);
	calc(pos[hi - 1]);

	lo = 1, hi = sz(pos);
	while(lo + 1 < hi) {
		int mid = (lo + hi) / 2;
		calc(pos[mid - 1]);
		if(dp1[a] < dp1[b]) lo = mid;
		else hi = mid;
	}

	calc(pos[lo - 1]);
	calc(pos[hi - 1]);
	cout << res;
}
 
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    //freopen(TASK".in" , "r" , stdin);
    //freopen(TASK".out" , "w" , stdout);
		
    int tc = 1;
    // cin >> tc;
    while(tc--) {
    	solve();
    }
    return 0;
}

• Subtask 1: 0 / 31
• Subtask 2: 69 / 69