Submission #577762

#	Time	Username	Problem	Language	Result	Execution time	Memory
577762		amunduzbaev	Star Trek (CEOI20_startrek)	C++17	38 / 100	91 ms	17112 KiB

startrek

#include "bits/stdc++.h"
using namespace std;
 
#define ar array
typedef int64_t ll;

const int N = 1e5 + 5;
const int mod = 1e9 + 7;
vector<int> edges[N];
int dp[N], sub[N], up[N];
int is[N][2], cnt[N];
ar<int, 2> C{};

void dfs(int u, int p = -1){
	cnt[u] = 1;
	for(auto x : edges[u]){
		if(x == p) continue;
		dfs(x, u);
		if(dp[x] == 0) dp[u] = 1;
		cnt[u] += cnt[x];
	}
	sub[u] = dp[u];
}

void re(int u, int p = -1){
	if(up[u] == 0) dp[u] = 1;
	ar<int, 2> c {};
	c[up[u]]++;
	for(auto x : edges[u]){
		if(x == p) continue;
		c[dp[x]]++;
	}
	
	for(auto x : edges[u]){
		if(x == p) continue;
		c[dp[x]]--;
		if(c[0]) up[x] = 1;
		c[dp[x]]++;
	}
	
	for(auto x : edges[u]){
		if(x == p) continue;
		re(x, u);
	}
}

int n;
void dfs2(int u, int p = -1){
	int f = 0, v = -1;
	for(auto x : edges[u]){
		if(x == p) continue;
		dfs2(x, u);
		if(!sub[x]){
			f++, v = x;
		}
	}
	
	if(f > 1){
		is[u][1] = cnt[u] * 1ll * n % mod;
	} else if(f == 1) {
		is[u][1] = (cnt[u] - cnt[v]) * 1ll * n % mod;
		is[u][1] = (is[u][1] + is[v][0]) % mod, is[u][0] = (is[u][0] + is[v][1]) % mod;
	} else {
		is[u][1] = C[0], is[u][0] = C[1];
		for(auto x : edges[u]){
			if(x == p) continue;
			is[u][0] = (is[u][0] + is[x][1]) % mod, is[u][1] = (is[u][1] + is[x][0]) % mod;
		}
	}
}

signed main(){
	ios::sync_with_stdio(0); cin.tie(0);
	
	int d; cin>>n>>d;
	for(int i=1;i<n;i++){
		int a, b; cin>>a>>b;
		edges[a].push_back(b);
		edges[b].push_back(a);
	}
	
	dfs(1);
	up[1] = 1;
	re(1);
	for(int i=1;i<=n;i++){
		C[dp[i]]++;
	}
	
	dfs2(1);
	cout<<is[1][1]<<"\n";
}

/*

5 1
1 2
2 3
2 4
1 5

*/

• Subtask 1: 0 / 0
• Subtask 2: 0 / 7
• Subtask 3: 8 / 8
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15