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Submission #379931

# Submission time Handle Problem Language Result Execution time Memory
379931 2021-03-19T17:58:14 Z AriaH Mousetrap (CEOI17_mousetrap) C++11
100 / 100
 1940 ms 260744 KB 
/** I can do this all day **/

#pragma GCC optimize("O2")
#include <bits/stdc++.h>
using namespace std;

typedef long long                   ll;
typedef long double                 ld;
typedef pair<int,int>               pii;
typedef pair<ll,ll>                 pll;
#define all(x)                      (x).begin(),(x).end()
#define F                           first
#define S                           second
#define Mp                          make_pair
#define SZ(x)			    		(int)x.size()
#define fast_io                     ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io                     freopen("in.txt" , "r+" , stdin) ; freopen("out.txt" , "w+" , stdout);

const int N = 1e6 + 10;
const ll mod = 1e9 + 7;
const ll mod2 = 998244353;
const ll inf = 8e18;
const int LOG = 22;

ll pw(ll a , ll b, ll M)  { return (!b ? 1 : (b & 1 ? (a * pw(a * a % M, b / 2, M)) % M : pw(a * a % M, b / 2, M))); }

int n, root,  m, dp[N], cost[N], P[LOG][N], H[N];

vector < int > G[N];

int LCA(int v, int u)
{
	if(H[v] > H[u]) swap(u, v);
	int del = H[u] - H[v];
	for(int T = 0; T < LOG; T ++) if(del >> T & 1) u = P[T][u];
	if(v == u) return v;
	for(int T = LOG - 1; ~T; T --)
	{
		if(P[T][v] ^ P[T][u])
		{
			u = P[T][u];
			v = P[T][v];
		}
	}
	return P[0][v];
}

void pre(int v)
{
	if(v ^ root)
	{
		cost[v] = cost[P[0][v]] + SZ(G[v]) - 1;
	}
	H[v] = H[P[0][v]] + 1;
	for(int T = 1; T < LOG; T ++) P[T][v] = P[T - 1][P[T - 1][v]];
	for(auto u : G[v])
	{
		if(u == P[0][v]) continue;
		P[0][u] = v;
		pre(u);
	}
}

void dfs(int v)
{
	if(v == root)
	{
		cost[v] = 0;
	}
	else
	{
		cost[v] = cost[v] - H[LCA(v, m)] + 1;
		if(LCA(v, m) == m) cost[v] ++;
	}
	int Mx1 = cost[v], Mx2 = cost[v], cnt = 0;
	for(auto u : G[v])
	{
		if(u == P[0][v]) continue;
		dfs(u);
		cnt ++;
		if(dp[u] > Mx1)
		{
			Mx2 = Mx1;
			Mx1 = dp[u];
		}
		else
		{
			Mx2 = max(Mx2, dp[u]);
		}
	}
	if(v == root)
	{
		dp[v] = 0;
		return;
	}
	if(cnt <= 1)
	{
		dp[v] = cost[v];
	}
	else
	{
		dp[v] = Mx2;
	}
}

bool check(int x)
{
	if(x < 0) return 0;
	int s = 1, node = m, bads = 0;
	for(auto u : G[node])
	{
		if(u == P[0][node]) continue;
		if(dp[u] > x)
		{
		    bads ++;
		}
	}
	s -= bads;
	x -= bads;
	if(s < 0 || x < 0) return 0;
	int last = m;
	node = P[0][node];
	s ++;
	while(node ^ root)
	{
		bads = 0;
		for(auto u : G[node])
		{
			if(u == last || u == P[0][node]) continue;
			if(dp[u] > x)
			{
			    bads ++;
			}
		}
		s -= bads;
		x -= bads;
		if(x < 0 || s < 0) return 0;
		last = node;
		node = P[0][node];
		s ++;
	}
	return 1;
}

int main()
{
	scanf("%d%d%d", &n, &root, &m);
	if(root == m) return !printf("0");
	for(int i = 1; i < n; i ++)
	{
		int a, b;
		scanf("%d%d", &a, &b);
		G[a].push_back(b);
		G[b].push_back(a);
	}
	pre(root);
	dfs(root);
	/*for(int i = 1; i <= n; i ++)
	{
		printf("i = %d cost : %d dp : %d\n", i, cost[i], dp[i]);
	}
	*/
	int d = -1, up = n + 10;
	while(up - d > 1)
	{
		int mid = (up + d) >> 1;
		if(check(mid))
		{
			up = mid;
		}
		else
		{
			d = mid;
		}
	}
	printf("%d", up);
	return 0;
}

/** test corner cases(n = 1?) watch for overflow or minus indices **/

Compilation message

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:147:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  147 |  scanf("%d%d%d", &n, &root, &m);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:152:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  152 |   scanf("%d%d", &a, &b);
      |   ~~~~~^~~~~~~~~~~~~~~~

Subtask #1
20.0 / 20.0

# Verdict Execution time Memory Grader output
1 Correct 16 ms 24044 KB Output is correct
2 Correct 16 ms 24044 KB Output is correct
3 Correct 16 ms 24044 KB Output is correct
4 Correct 16 ms 24044 KB Output is correct
5 Correct 15 ms 24044 KB Output is correct
6 Correct 15 ms 24044 KB Output is correct
7 Correct 15 ms 24044 KB Output is correct
8 Correct 16 ms 24044 KB Output is correct
9 Correct 15 ms 24044 KB Output is correct
10 Correct 16 ms 24044 KB Output is correct

Subtask #2
25.0 / 25.0

# Verdict Execution time Memory Grader output
1 Correct 604 ms 153068 KB Output is correct
2 Correct 557 ms 140140 KB Output is correct
3 Correct 1561 ms 154092 KB Output is correct
4 Correct 724 ms 89324 KB Output is correct
5 Correct 1545 ms 154204 KB Output is correct
6 Correct 1554 ms 154092 KB Output is correct

Subtask #3
20.0 / 20.0

# Verdict Execution time Memory Grader output
1 Correct 16 ms 24044 KB Output is correct
2 Correct 16 ms 24044 KB Output is correct
3 Correct 16 ms 24044 KB Output is correct
4 Correct 16 ms 24044 KB Output is correct
5 Correct 15 ms 24044 KB Output is correct
6 Correct 15 ms 24044 KB Output is correct
7 Correct 15 ms 24044 KB Output is correct
8 Correct 16 ms 24044 KB Output is correct
9 Correct 15 ms 24044 KB Output is correct
10 Correct 16 ms 24044 KB Output is correct
11 Correct 16 ms 24044 KB Output is correct
12 Correct 16 ms 24172 KB Output is correct
13 Correct 17 ms 24172 KB Output is correct
14 Correct 19 ms 24336 KB Output is correct
15 Correct 17 ms 24172 KB Output is correct
16 Correct 16 ms 24172 KB Output is correct
17 Correct 19 ms 24172 KB Output is correct
18 Correct 19 ms 24172 KB Output is correct
19 Correct 16 ms 24172 KB Output is correct
20 Correct 17 ms 24192 KB Output is correct
21 Correct 17 ms 24140 KB Output is correct
22 Correct 16 ms 24044 KB Output is correct

Subtask #4
35.0 / 35.0

# Verdict Execution time Memory Grader output
1 Correct 16 ms 24044 KB Output is correct
2 Correct 16 ms 24044 KB Output is correct
3 Correct 16 ms 24044 KB Output is correct
4 Correct 16 ms 24044 KB Output is correct
5 Correct 15 ms 24044 KB Output is correct
6 Correct 15 ms 24044 KB Output is correct
7 Correct 15 ms 24044 KB Output is correct
8 Correct 16 ms 24044 KB Output is correct
9 Correct 15 ms 24044 KB Output is correct
10 Correct 16 ms 24044 KB Output is correct
11 Correct 604 ms 153068 KB Output is correct
12 Correct 557 ms 140140 KB Output is correct
13 Correct 1561 ms 154092 KB Output is correct
14 Correct 724 ms 89324 KB Output is correct
15 Correct 1545 ms 154204 KB Output is correct
16 Correct 1554 ms 154092 KB Output is correct
17 Correct 16 ms 24044 KB Output is correct
18 Correct 16 ms 24172 KB Output is correct
19 Correct 17 ms 24172 KB Output is correct
20 Correct 19 ms 24336 KB Output is correct
21 Correct 17 ms 24172 KB Output is correct
22 Correct 16 ms 24172 KB Output is correct
23 Correct 19 ms 24172 KB Output is correct
24 Correct 19 ms 24172 KB Output is correct
25 Correct 16 ms 24172 KB Output is correct
26 Correct 17 ms 24192 KB Output is correct
27 Correct 17 ms 24140 KB Output is correct
28 Correct 16 ms 24044 KB Output is correct
29 Correct 16 ms 24044 KB Output is correct
30 Correct 672 ms 166460 KB Output is correct
31 Correct 747 ms 166508 KB Output is correct
32 Correct 780 ms 260744 KB Output is correct
33 Correct 702 ms 260508 KB Output is correct
34 Correct 1794 ms 167476 KB Output is correct
35 Correct 1770 ms 167404 KB Output is correct
36 Correct 1927 ms 176748 KB Output is correct
37 Correct 1940 ms 176892 KB Output is correct
38 Correct 1730 ms 179460 KB Output is correct
39 Correct 1697 ms 179476 KB Output is correct
40 Correct 1693 ms 179752 KB Output is correct