Submission #349215

#	Time	Username	Problem	Language	Result	Execution time	Memory
349215		arnold518	Mousetrap (CEOI17_mousetrap)	C++14	25 / 100	1039 ms	64108 KiB

mousetrap

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

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int MAXN = 1e6;

int N, R, X;
vector<int> adj[MAXN+10];

vector<int> V;
bool P[MAXN+10];
int val[MAXN+10];

int dfs(int now, int bef)
{
	V.push_back(now);
	if(now==X) return 1;
	for(int nxt : adj[now])
	{
		if(nxt==bef) continue;
		if(dfs(nxt, now)) return 1;
	}
	V.pop_back();
	return 0;
}

void dfs2(int now, int bef)
{
	int chd=0;
	for(int nxt : adj[now])
	{
		if(nxt==bef) continue;
		if(P[nxt]) continue;
		chd++;
	}
	val[now]=val[bef]+chd;
	for(int nxt : adj[now])
	{
		if(nxt==bef) continue;
		if(P[nxt]) continue;
		dfs2(nxt, now);
	}
}

int dp[MAXN+10];

void dfs3(int now, int bef)
{
	int a=0, b=0, cnt=0;
	for(int nxt : adj[now])
	{
		if(nxt==bef) continue;
		if(P[nxt]) continue;
		dfs3(nxt, now);
		cnt++;
		if(a<=dp[nxt]) b=a, a=dp[nxt];
		else if(b<=dp[nxt]) b=dp[nxt];
	}
	dp[now]=b;
	if(cnt<=1) dp[now]=val[now];
}

int main()
{
	scanf("%d%d%d", &N, &R, &X);
	for(int i=1; i<N; i++)
	{
		int u, v;
		scanf("%d%d", &u, &v);
		adj[u].push_back(v);
		adj[v].push_back(u);
	}

	dfs(R, R);
	for(auto it : V) P[it]=1;
	int t=0;
	for(int i=1; i<V.size(); i++)
	{
		dfs2(V[i], V[i]);
		if(i+1<V.size())
		{
			t+=adj[V[i]].size()-2;
			val[V[i+1]]=t;
		}
	}

	for(int i=1; i<V.size(); i++)
	{
		dfs3(V[i], V[i]);
		dp[V[i]]=0;

		int a=0, b=0, cnt=0;
		for(int nxt : adj[V[i]])
		{
			if(P[nxt]) continue;
			if(a<=dp[nxt]) b=a, a=dp[nxt];
			else if(b<=dp[nxt]) b=dp[nxt];
		}
		dp[V[i]]=min(max(a, dp[V[i-1]]), max(b, dp[V[i-1]]+1));
	}
	printf("%d\n", dp[X]);

	//dfs(X, R, adj[X].size());
	//printf("%d\n", dp[X]-1);
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:80:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   80 |  for(int i=1; i<V.size(); i++)
      |               ~^~~~~~~~~
mousetrap.cpp:83:9: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |   if(i+1<V.size())
      |      ~~~^~~~~~~~~
mousetrap.cpp:90:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   90 |  for(int i=1; i<V.size(); i++)
      |               ~^~~~~~~~~
mousetrap.cpp:95:17: warning: unused variable 'cnt' [-Wunused-variable]
   95 |   int a=0, b=0, cnt=0;
      |                 ^~~
mousetrap.cpp:68:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   68 |  scanf("%d%d%d", &N, &R, &X);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:72:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   72 |   scanf("%d%d", &u, &v);
      |   ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 20
• Subtask 2: 25 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35