Submission #303060

#	Time	Username	Problem	Language	Result	Execution time	Memory
303060		Kenzo_1114	Mousetrap (CEOI17_mousetrap)	C++17	45 / 100	911 ms	64148 KiB

mousetrap

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 1000010;

int n, t, m, dp[MAXN], par[MAXN];
vector<int> graph[MAXN];

void dfs(int v, int p)
{	
	int mx[2] = {-1, -1};
	par[v] = p;

	for(int i = 0; i < graph[v].size(); i++)
	{
		int u = graph[v][i];
		if(u == p)	continue;

		dfs(u, v);
		if(dp[u] >= mx[0])	mx[1] = mx[0], mx[0] = dp[u];
		else if(dp[u] > mx[1])	mx[1] = dp[u];
	}

	dp[v] = ((int) graph[v].size() == 2) ? 1 : mx[1] + graph[v].size() - 1;
	if((int) graph[v].size() == 1)	dp[v] = 0;
}

int main ()
{
	scanf("%d %d %d", &n, &t, &m);

	for(int i = 0, u, v; i < n - 1; i++)
	{
		scanf("%d %d", &u, &v);
		graph[u].push_back(v);
		graph[v].push_back(u);
	}

	if(t == m || (int) graph[m].size() == 0)
	{	printf("0\n"); return 0;	}

	dfs(t, t);

	int cur = m, ans = dp[m];
	while(true) 
	{
		cur = par[cur];
		if(cur == t)	break;
		ans += (int) graph[cur].size() - 2;
	}

//	for(int i = 1; i <= n; i++)	printf("dp[%d] = %d\n", i, dp[i]);

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

/*

10 1 4
1 2
2 3
2 4
3 9
3 5
4 7
4 6
6 8
7 10

*/

Compilation message (stderr)

mousetrap.cpp: In function 'void dfs(int, int)':
mousetrap.cpp:13:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |  for(int i = 0; i < graph[v].size(); i++)
      |                 ~~^~~~~~~~~~~~~~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:29:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   29 |  scanf("%d %d %d", &n, &t, &m);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:33:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   33 |   scanf("%d %d", &u, &v);
      |   ~~~~~^~~~~~~~~~~~~~~~~

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