Submission #127070

#	Time	Username	Problem	Language	Result	Execution time	Memory
127070		Lawliet	Mousetrap (CEOI17_mousetrap)	C++14	25 / 100	1209 ms	68044 KiB

mousetrap

#include <bits/stdc++.h>

#define MAX 1000010

using namespace std;
typedef long long int lli;

int n;
int mouse, trap;
int n1, n2;

int pai[MAX];

lli dp[MAX];

vector<int> grafo[MAX];

void DFSInit(int i, int p)
{
	for(int g = 0 ; g < grafo[i].size() ; g++)
	{
		int prox = grafo[i][g];

		if(prox == p) continue;

		pai[prox] = i;

		DFSInit(prox , i);
	}
}

void DFS(int i, int p, int blockI, int blockProx)
{
	if(grafo[i].size() == 1 && i != trap)
	{
		dp[i] = 0;
		return;
	}

	vector<int> aux;

	aux.push_back( 0 );

	for(int g = 0 ; g < grafo[i].size() ; g++)
	{
		int prox = grafo[i][g];

		if(prox == p) continue;

		if(blockI == i && blockProx == prox) continue;

		pai[prox] = i;

		//printf("i = %d  prox = %d\n",i,prox);

		DFS(prox , i , blockI , blockProx);

		aux.push_back( dp[prox] );
	}

	sort(aux.begin() , aux.end());

	dp[i] = grafo[i].size() - 2 + aux[aux.size() - 2] + 1;

	if(i == blockI) dp[i]--;

	//printf("dp(%d) = %lld\n",i,dp[i]);
}

int main()
{
	scanf("%d %d %d",&n,&trap,&mouse);

	for(int g = 0 ; g < n - 1 ; g++)
	{
		scanf("%d %d",&n1,&n2);

		grafo[n1].push_back(n2);
		grafo[n2].push_back(n1);
	}

	DFSInit(trap , trap);

	DFS(trap , trap , 0 , 0);

	int aux = pai[mouse];
	int sum = 0;

	while(aux != trap)
	{
		sum += grafo[aux].size() - 2;
		aux = pai[aux];
	}

	//printf("dp = %d  sum = %d\n",dp[mouse],sum);

	lli ans = dp[mouse] + sum;

	int cur = pai[mouse];
	int last = mouse;
	//int sum = 0;

	while(cur != trap)
	{
		DFS(trap , trap , cur , last);

		//printf("cur = %d\n",cur);

		aux = pai[cur];
		sum = 0;

		while(aux != trap)
		{
			sum += grafo[aux].size() - 2;
			aux = pai[aux];
		}

		//printf("dp = %d  sum = %d\n",dp[cur],sum);

		ans = max(ans , dp[cur] + sum);

		last = cur;
		cur = pai[last];
	}

	printf("%lld\n",ans);
}

Compilation message (stderr)

mousetrap.cpp: In function 'void DFSInit(int, int)':
mousetrap.cpp:20:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int g = 0 ; g < grafo[i].size() ; g++)
                  ~~^~~~~~~~~~~~~~~~~
mousetrap.cpp: In function 'void DFS(int, int, int, int)':
mousetrap.cpp:44:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int g = 0 ; g < grafo[i].size() ; g++)
                  ~~^~~~~~~~~~~~~~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:72:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d %d",&n,&trap,&mouse);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:76:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d",&n1,&n2);
   ~~~~~^~~~~~~~~~~~~~~~~

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