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답안 #116156

# 제출 시각 아이디 문제 언어 결과 실행 시간 메모리
116156 2019-06-11T03:31:14 Z user202729 Mousetrap (CEOI17_mousetrap) C++17
45 / 100
 2840 ms 72668 KB 
// https://oj.uz/problem/view/CEOI17_mousetrap
#ifndef _GLIBCXX_DEBUG
#define NDEBUG
#endif

#include<iostream>
#include<vector>
#include<queue>
#include<algorithm>
#include<functional>
#include<cassert>

int nn,trap,mouse;
std::vector<std::vector<int>> ad;

std::vector<int> par; // with root = trap
std::vector<int> nrock; // num of rock to put if mouse is trapped at [?]
// of course the mouse can only be trapped at nodes with <= 1 child (rooted somewhere)
void dfs1(int x){
	int const px=par[x];
	nrock[x]=nrock[px]+ad[x].size()-2;
	for(int child:ad[x])if(child!=px){
		par[child]=x;
		dfs1(child);
	}
}

std::vector<int> d1; // dist(?, line(trap, mouse))

std::vector<int> cost; // total cost if mouse is trapped at [?] = nrock + d1

int thr;
bool dfs3(int x,int par){ // is it possible to force mouse to be trapped at a node with cost <= thr ...
	// when start at x?
	// if(x==trap)return true;
	int nchild=ad[x].size()-(par>=0);
	if(nchild==0)return cost[x]<=thr;
	if(nchild==1){ // not sure about this, what if deg(mouse) == 1?
		if(cost[x]<=thr)return true;
		return false; // ???
	}
	int n_impos=0;
	for(int child:ad[x])if(child!=par){
		bool ans=dfs3(child,x);
		assert(std::cerr<<child+1<<' '<<x+1<<" dfs3-> "<<ans<<'\n');
		n_impos+=!ans;
	}
	return n_impos<=1;
}

int main(){
	std::ios::sync_with_stdio(false);std::cin.tie(nullptr);
	std::cin>>nn>>trap>>mouse;
	if(trap==mouse){
		std::cout<<"0\n";
		return 0;
	}
	--trap;--mouse;
	ad.resize(nn);
	for(int u,v,_=nn-1;_--;){
		std::cin>>u>>v;--u;--v;
		ad[u].push_back(v);
		ad[v].push_back(u);
	}
	nrock.resize(nn);nrock[trap]=1;
	par.resize(nn);par[trap]=-1;
	for(int x:ad[trap]){
		par[x]=trap;
		dfs1(x);
	}

	d1.resize(nn,-1);
	std::queue<int> q;
	for(int x=mouse;x>=0;x=par[x]){
		q.push(x);
		d1[x]=0;
		if(par[x]==trap){
			ad[trap].assign(1,x); // remove unnecessary edges
		}
	}
	while(!q.empty()){
		int const x=q.front();q.pop();
		int const newd=d1[x]+1;assert(newd>0);
		for(int y:ad[x])if(d1[y]<0){
			d1[y]=newd;
			q.push(y);
		}
	}

	cost.resize(nn);
	std::transform(begin(nrock),end(nrock),begin(d1),begin(cost),std::plus<int>{});

	thr=nn;
	for(int r=1<<29;r;r>>=1){
		if(thr-r<0)continue;
		thr-=r;
		if(!dfs3(mouse,-1))
			thr+=r;
	}
	std::cout<<thr<<'\n';
	return 0;
}

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

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

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

Subtask #1
20.0 / 20.0

# 결과 실행 시간 메모리 Grader output
1 Correct 2 ms 384 KB Output is correct
2 Correct 2 ms 384 KB Output is correct
3 Correct 2 ms 384 KB Output is correct
4 Correct 2 ms 384 KB Output is correct
5 Correct 2 ms 384 KB Output is correct
6 Correct 2 ms 256 KB Output is correct
7 Correct 2 ms 384 KB Output is correct
8 Correct 2 ms 384 KB Output is correct
9 Correct 2 ms 384 KB Output is correct
10 Correct 2 ms 384 KB Output is correct

Subtask #2
25.0 / 25.0

# 결과 실행 시간 메모리 Grader output
1 Correct 505 ms 72668 KB Output is correct
2 Correct 497 ms 65656 KB Output is correct
3 Correct 2357 ms 72560 KB Output is correct
4 Correct 1177 ms 36440 KB Output is correct
5 Correct 2551 ms 72540 KB Output is correct
6 Correct 2840 ms 72592 KB Output is correct

Subtask #3
0 / 20.0

# 결과 실행 시간 메모리 Grader output
1 Correct 2 ms 384 KB Output is correct
2 Correct 2 ms 384 KB Output is correct
3 Correct 2 ms 384 KB Output is correct
4 Correct 2 ms 384 KB Output is correct
5 Correct 2 ms 384 KB Output is correct
6 Correct 2 ms 256 KB Output is correct
7 Correct 2 ms 384 KB Output is correct
8 Correct 2 ms 384 KB Output is correct
9 Correct 2 ms 384 KB Output is correct
10 Correct 2 ms 384 KB Output is correct
11 Correct 2 ms 384 KB Output is correct
12 Correct 2 ms 384 KB Output is correct
13 Correct 3 ms 384 KB Output is correct
14 Correct 3 ms 512 KB Output is correct
15 Correct 2 ms 512 KB Output is correct
16 Correct 2 ms 384 KB Output is correct
17 Incorrect 2 ms 512 KB Output isn't correct
18 Halted 0 ms 0 KB -

Subtask #4
0 / 35.0

# 결과 실행 시간 메모리 Grader output
1 Correct 2 ms 384 KB Output is correct
2 Correct 2 ms 384 KB Output is correct
3 Correct 2 ms 384 KB Output is correct
4 Correct 2 ms 384 KB Output is correct
5 Correct 2 ms 384 KB Output is correct
6 Correct 2 ms 256 KB Output is correct
7 Correct 2 ms 384 KB Output is correct
8 Correct 2 ms 384 KB Output is correct
9 Correct 2 ms 384 KB Output is correct
10 Correct 2 ms 384 KB Output is correct
11 Correct 505 ms 72668 KB Output is correct
12 Correct 497 ms 65656 KB Output is correct
13 Correct 2357 ms 72560 KB Output is correct
14 Correct 1177 ms 36440 KB Output is correct
15 Correct 2551 ms 72540 KB Output is correct
16 Correct 2840 ms 72592 KB Output is correct
17 Correct 2 ms 384 KB Output is correct
18 Correct 2 ms 384 KB Output is correct
19 Correct 3 ms 384 KB Output is correct
20 Correct 3 ms 512 KB Output is correct
21 Correct 2 ms 512 KB Output is correct
22 Correct 2 ms 384 KB Output is correct
23 Incorrect 2 ms 512 KB Output isn't correct
24 Halted 0 ms 0 KB -