Submission #349231

#	Time	Username	Problem	Language	Result	Execution time	Memory
349231		arnold518	Mousetrap (CEOI17_mousetrap)	C++14	20 / 100	48 ms	4972 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 = 1000;
const int INF = 987654321;

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][MAXN+10];

void dfs3(int now, int bef)
{
	if(now==R) return;

	for(int i=0; i<=N; i++) dp[now][i]=INF;
	if(P[now])
	{
		vector<int> V[MAXN+10];

		int pnode=-1;
		int chd=0;
		for(int nxt : adj[now])
		{
			if(nxt==bef) continue;
			if(P[nxt])
			{
				pnode=nxt;
				dfs3(nxt, now);
				continue;
			}
			chd++;
			dfs3(nxt, now);
			for(int i=0; i<=N; i++) V[i].push_back(dp[nxt][i]);
		}	
		assert(pnode!=-1);
		for(int i=0; i<=N; i++) sort(V[i].begin(), V[i].end(), greater<int>());
		for(int i=0; i<N; i++) for(int j=0; j<V[i+1].size(); j++)
		{
			if(i+j<=N) dp[now][i+j]=min(dp[now][i+j], max(V[i+1][j], dp[pnode][i+1]+j));
		}
		for(int i=chd; i-chd+1<=N; i++) dp[now][i]=min(dp[now][i], dp[pnode][i-chd+1]+chd);
	}
	else
	{
		vector<int> V[MAXN+10];

		int chd=0;
		for(int nxt : adj[now])
		{
			if(nxt==bef) continue;
			chd++;
			dfs3(nxt, now);
			for(int i=0; i<=N; i++) V[i].push_back(dp[nxt][i]);
		}	
		for(int i=0; i<=N; i++) sort(V[i].begin(), V[i].end(), greater<int>());
		for(int i=0; i<N; i++) for(int j=0; j<V[i+1].size(); j++)
		{
			if(i+j<=N) dp[now][i+j]=min(dp[now][i+j], V[i+1][j]);
		}
		for(int i=chd; i<=N; i++) dp[now][i]=min(dp[now][i], val[now]);
	}
	
	//printf("%d : ", now);
	//for(int i=0; i<=N; i++) printf("%d ", dp[now][i]); printf("\n");
}

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;
		}
	}
	dfs3(X, X);
	printf("%d\n", dp[X][1]);
	//dfs(X, R, adj[X].size());
	//printf("%d\n", dp[X]-1);
}

Compilation message (stderr)

mousetrap.cpp: In function 'void dfs3(int, int)':
mousetrap.cpp:77:40: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   77 |   for(int i=0; i<N; i++) for(int j=0; j<V[i+1].size(); j++)
      |                                       ~^~~~~~~~~~~~~~
mousetrap.cpp:96:40: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   96 |   for(int i=0; i<N; i++) for(int j=0; j<V[i+1].size(); j++)
      |                                       ~^~~~~~~~~~~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:121:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  121 |  for(int i=1; i<V.size(); i++)
      |               ~^~~~~~~~~
mousetrap.cpp:124:9: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  124 |   if(i+1<V.size())
      |      ~~~^~~~~~~~~
mousetrap.cpp:109:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  109 |  scanf("%d%d%d", &N, &R, &X);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:113:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  113 |   scanf("%d%d", &u, &v);
      |   ~~~~~^~~~~~~~~~~~~~~~

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