Submission #415201

#	Time	Username	Problem	Language	Result	Execution time	Memory
415201		amunduzbaev	The Xana coup (BOI21_xanadu)	C++14	100 / 100	145 ms	30824 KiB

xanadu

/* made by amunduzbaev */

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

using namespace std;
//~ using namespace __gnu_pbds;

#define ff first
#define ss second
#define vv vector
#define pb push_back
#define mp make_pair
#define ub upper_bound
#define lb lower_bound
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(),x.rend()
#define mem(arr, v) memset(arr, v, sizeof arr)
#define NeedForSpeed ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define int long long

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vii;
typedef vector<pii> vpii;
template<class T> bool umin(T& a, const T& b) { return a > b ? a = b, true : false; }
template<class T> bool umax(T& a, const T& b) { return a < b ? a = b, true : false; }
template<int sz> using tut = array<int, sz>;
void usaco(string s) { freopen((s+".in").c_str(),"r",stdin);
  freopen((s+".out").c_str(),"w",stdout); NeedForSpeed }
//~ template<class T> using oset = tree<T,
//~ null_type, less_equal<T>, rb_tree_tag,
//~ tree_order_statistics_node_update> ordered_set;

const int N = 2e5+5;
const int mod = 1e9+7;
const ll inf = 1e18;
const ld Pi = acos(-1);

#define MULTI 0
int n, m, k, s, t, q, ans, res, a[N];
int dp[N][2][2];
vii edges[N];

void dfs(int u, int p = -1){
	vii ch;
	for(auto x : edges[u]){
		if(x == p) continue;
		ch.pb(x), dfs(x, u);
	} 
	if(!sz(ch)) dp[u][a[u]][0] = 0, dp[u][a[u] ^ 1][1] = 1;
	else if(sz(ch) == 1){ int x = ch[0];
		umin(dp[u][a[u]][0], dp[x][0][0]);
		umin(dp[u][a[u]][1], dp[x][1][1] + 1);
		umin(dp[u][a[u]^1][0], dp[x][0][1]);
		umin(dp[u][a[u]^1][1], dp[x][1][0] + 1);
	} else if(sz(ch) == 2){
		int lx = ch[0], rx = ch[1];
		umin(dp[u][a[u]][0], min(dp[lx][0][0] + dp[rx][0][0], dp[lx][0][1] + dp[rx][0][1]));
		umin(dp[u][a[u]][1], min(dp[lx][1][0] + dp[rx][1][1], dp[lx][1][1] + dp[rx][1][0]) + 1);
		umin(dp[u][a[u]^1][0], min(dp[lx][0][1] + dp[rx][0][0], dp[lx][0][0] + dp[rx][0][1]));
		umin(dp[u][a[u]^1][1], min(dp[lx][1][1] + dp[rx][1][1], dp[lx][1][0] + dp[rx][1][0]) + 1);
	} else {
		vpii tt;
		int sum = 0;
		// vertex u, color a[u], not using itself
		for(auto x : ch) sum += dp[x][0][0], tt.pb({dp[x][0][1] - dp[x][0][0], x});
		sort(all(tt));
		umin(dp[u][a[u]][0], sum);
		for(int i=1;i<sz(ch);i+=2) sum += tt[i].ff + tt[i-1].ff, umin(dp[u][a[u]][0], sum);
		
		// vertex u, color a[u], using itself
		tt.clear(); sum = 0; 
		for(auto x : ch) sum += dp[x][1][0], tt.pb({dp[x][1][1] - dp[x][1][0], x});
		sort(all(tt));
		sum += tt[0].ff;
		umin(dp[u][a[u]][1], sum + 1);
		for(int i=2;i<sz(tt);i+=2) sum += tt[i].ff, sum += tt[i-1].ff, umin(dp[u][a[u]][1], sum + 1);
		
		//vertex u, color a[u]^1, not using itself
		tt.clear(); sum = 0; 
		for(auto x : ch) sum += dp[x][0][0], tt.pb({dp[x][0][1] - dp[x][0][0], x});
		sort(all(tt));
		sum += tt[0].ff;
		umin(dp[u][a[u]^1][0], sum);
		for(int i=2;i<sz(tt);i+=2) sum += tt[i].ff, sum += tt[i-1].ff, umin(dp[u][a[u]^1][0], sum);
		
		// vertex u, color a[u]^1, using itself
		tt.clear(); sum = 0; 
		for(auto x : ch) sum += dp[x][1][0], tt.pb({dp[x][1][1] - dp[x][1][0], x});
		sort(all(tt));
		umin(dp[u][a[u]^1][1], sum + 1);
		for(int i=1;i<sz(tt);i+=2) sum += tt[i].ff, sum += tt[i-1].ff, umin(dp[u][a[u]^1][1], sum + 1);
	}
}

/*

5
1 2 
2 3
3 4
4 5
0 1 1 1 1

*/

void solve(int t_case){
	cin>>n;
	for(int i=1;i<n;i++){
		int a, b; cin>>a>>b;
		edges[a].pb(b), edges[b].pb(a);
	} for(int i=1;i<=n;i++) cin>>a[i];
	int root = 1;
	for(int i=1;i<=n;i++) dp[i][0][0] = dp[i][0][1] = dp[i][1][0] = dp[i][1][1] = mod;
	for(int i=1;i<=n;i++) if(sz(edges[i]) <= 2ll) { root = i; break; }
	dfs(root);
	
	int res = min(dp[root][0][0], dp[root][0][1]);
	if(res == mod) cout<<"impossible\n"; 
	else cout<<res<<"\n";
}

signed main(){
	NeedForSpeed
	if(MULTI){
		int t; cin>>t;
		for(int t_case = 1; t_case <= t; t_case++) solve(t_case);
	} else solve(1);
	return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'void usaco(std::string)':
xanadu.cpp:33:31: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   33 | void usaco(string s) { freopen((s+".in").c_str(),"r",stdin);
      |                        ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xanadu.cpp:34:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   34 |   freopen((s+".out").c_str(),"w",stdout); NeedForSpeed }
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30