Submission #144773

#	Time	Username	Problem	Language	Result	Execution time	Memory
144773		liwi	Mousetrap (CEOI17_mousetrap)	C++11	100 / 100	1732 ms	151212 KiB

mousetrap

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;

#define scan(x) do{while((x=getchar())<'0'); for(x-='0'; '0'<=(_=getchar()); x=(x<<3)+(x<<1)+_-'0');}while(0)
char _;
#define complete_unique(a) a.erase(unique(a.begin(),a.end()),a.end())
#define all(a) a.begin(),a.end()
#define println printf("\n");
#define readln(x) getline(cin,x);
#define pb push_back
#define endl "\n"
#define INT_INF 0x3f3f3f3f
#define LL_INF 0x3f3f3f3f3f3f3f3f
#define MOD 1000000007
#define MOD2 1190492669
#define SEED 131
#define mp make_pair
#define fastio cin.tie(0); cin.sync_with_stdio(0);

#define MAXN 1000005

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef unordered_map<int,int> umii;
typedef pair<int,int> pii;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef pair<int,pii> triple;
typedef int8_t byte;

mt19937 g1(time(0));

int randint(int a, int b){return uniform_int_distribution<int>(a, b)(g1);}
ll randlong(ll a,ll b){return uniform_int_distribution<long long>(a, b)(g1);}

ll gcd(ll a, ll b){return b == 0 ? a : gcd(b, a % b);}
ll lcm(ll a, ll b){return a*b/gcd(a,b);}
ll fpow(ll  b, ll exp, ll mod){if(exp == 0) return 1;ll t = fpow(b,exp/2,mod);if(exp&1) return t*t%mod*b%mod;return t*t%mod;}
ll divmod(ll i, ll j, ll mod){i%=mod,j%=mod;return i*fpow(j,mod-2,mod)%mod;}

int num_nodes,T,M,dp[MAXN],par[MAXN],depth[MAXN],sum[MAXN];
bool done[MAXN],marked[MAXN];
vector<int> connections[MAXN];

inline bool cmp(int a, int b){
	return depth[a]>depth[b];
}

int dfs(int node, int prev){
	for(int check:connections[node]){
		if(check == prev) continue;
		par[check] = node;
		depth[check] = depth[node]+1;
		dfs(check,node);
	}
}

int solve(int node, int prev){
	int bst = -1, bst2 = -1, cnt = 0;
	for(int check:connections[node]){
		if(check == prev) continue;
		cnt++;
	}
	sum[node] = sum[prev]+cnt;
	for(int check:connections[node]){
		if(check == prev) continue;
		int n = solve(check,node);
		if(n >= bst) bst2 = bst, bst = n;
		else if(n > bst2) bst2 = n;
	}
	if(cnt == 0) return dp[node] = 0;
	if(bst2 == -1) return dp[node] = 1;
	return dp[node] = bst2+cnt;
}

bool works(int mid){
	memset(done,false,sizeof done);
	deque<int> v;
	int current = M, cnt = 0, og = 0;
	while(current != T){
		int mm = 0;
		for(int check:connections[current]){
			if(check == par[current] || marked[check]) continue;
			int cost = cnt+sum[current]+dp[check]-depth[current]-(current!=M);
			if(cost > mid){
				v.pb(check);
				mm++;
			}else done[check] = true;
		}
		cnt+=mm, og+=mm;
		current = par[current];
	}
	sort(all(v),cmp);
	current = M;
	while(current != T){
		if(v.size()){
			int n = v.front(); v.pop_front();
			done[n] = true;
		}
		for(int check:connections[current]){
			if(check == par[current] || done[check] || marked[check]) continue;
			return false;
		}
		current = par[current];
	}
	if(og <= mid) return true;
	return false;
}

int main(){
	scanf("%d %d %d",&num_nodes,&T,&M);
	for(int i=1; i<num_nodes; i++){
		int a,b; scanf(" %d %d",&a,&b);
		connections[a].pb(b);
		connections[b].pb(a);
	}
	dfs(T,-1);
	solve(T,-1);
	int curr = M;
	while(curr){
		marked[curr] = true;
		curr = par[curr];
	}
	int low = 0, high = 2*num_nodes, ans = high;
	while(low <= high){
		int mid = (low+high)/2;
		if(works(mid)){
			ans = mid;
			high = mid-1;
		}else low = mid+1;
	}
	printf("%d\n",ans);
}
/*
3 1 3
1 2
2 3
ans=0
 */

Compilation message (stderr)

mousetrap.cpp: In function 'int dfs(int, int)':
mousetrap.cpp:62:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:117:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d %d",&num_nodes,&T,&M);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:119:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   int a,b; scanf(" %d %d",&a,&b);
            ~~~~~^~~~~~~~~~~~~~~~

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