Submission #1118502

#	Time	Username	Problem	Language	Result	Execution time	Memory
1118502		Peter2017	Torrent (COI16_torrent)	C++14	69 / 100	630 ms	40804 KiB

torrent

#include <bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define pii pair<int,int>
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
#define mem(a, b) memset(a, b, sizeof(a))
#define name "test"

using namespace std;

const int N = 3e5 + 5;
const int mod = 1e9 + 7;

template <typename T1, typename T2> bool maxi(T1 &a, T2 b){if (a < b){a = b; return 1;} return 0;}
template <typename T1, typename T2> bool mini(T1 &a, T2 b){if (a > b){a = b; return 1;} return 0;}

int n;
int s;
int t;
bool stop[N];
vector<int> path;
vector<int> dp[N];
vector<int> adj[N];

void load(){
	cin.tie(0)->sync_with_stdio(0);
	if (fopen(name".inp", "r")){
		freopen(name".inp", "r", stdin);
		freopen(name".out", "w", stdout);
	}
}

void input(){
	cin >> n >> s >> t;
	for (int i = 1; i < n; i++){
		int u, v; cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
}

bool getPath(int u, int pre){
	if (u == t){
		path.push_back(u);
		return 1;
	}
	for (int v : adj[u]) if (v != pre){
		if (getPath(v, u)){
			path.push_back(u);
			return 1;
		}
	}
	return 0;
}

int dfs(int u, int pre, bool type){
	dp[u].clear();
	for (int v : adj[u]) if (v != pre && !stop[v]){
		dp[u].push_back(dfs(v, u, type));
	}
	sort(dp[u].begin(), dp[u].end(), greater<int>());
	int res = 0;
	for (int i = 0; i < (int)dp[u].size(); i++)
		maxi(res, dp[u][i] + i + 1);
	return res;
}

int cal(int j){
	int ans = 0;
	stop[path[j + 1]] = 1;
	ans = dfs(s, 0, 0);
	stop[path[j + 1]] = 0;
	stop[path[j]] = 1;
	maxi(ans, dfs(t, 0, 1));
	stop[path[j]] = 0;
	return ans;
}

void solve(){
	if (s == t){
		assert(false);
		cout << dfs(s, 0, 0);
		return;
	}
	getPath(s, 0);
	reverse(path.begin(), path.end());
	int ans = cal(0);
	int l = 0, r = (int)path.size() - 2;
	while (l < r){
		int m1 = (l + r) >> 1;
		int m2 = m1 + 1;
		int tmp1 = cal(m1);
		int tmp2 = cal(m2);
		mini(ans, min(tmp1, tmp2));
		if (tmp1 <= tmp2) r = m1;
		else l = m2;
	}
	cout << ans;
}

int main(){
	load();
	input();
	solve();
}

Compilation message (stderr)

torrent.cpp: In function 'void load()':
torrent.cpp:30:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |   freopen(name".inp", "r", stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:31:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   31 |   freopen(name".out", "w", stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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