Submission #1225057

#	Time	Username	Problem	Language	Result	Execution time	Memory
1225057		wedonttalkanymore	The Xana coup (BOI21_xanadu)	C++20	0 / 100	74 ms	21828 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

const int inf = 1e9;

int n, a[100005];
vector <int> adj[100005];
int dp[100005][2][2];

void dfs(int u, int par) {
	for (auto v : adj[u]) {
		if (v != par) {
			dfs(v, u);
		}
	}
	vector <int> child;
	child.push_back(-1);
	for (auto v : adj[u]) {
		if (v != par) {
			child.push_back(v);
		}
	}
	int f[child.size()][2][2]; // xet den con child[i], switch hay khong, chan hay le(0 chan 1 le)
	for (int p = 0; p < 2; p++) for (int j = 0; j < 2; j++) f[0][p][j] = inf;
	f[0][0][a[u]] = 0, f[0][0][a[u] ^ 1] = 0;
	for (int i = 1; i < child.size(); i++) {
		for (int j = 0; j <= 1; j++) {
			f[i][0][j] = min(f[i - 1][0][j ^ 1] + dp[child[i]][1][0], f[i - 1][0][j] + dp[child[i]][0][0]);
			f[i][1][j] = min(f[i - 1][1][j ^ 1] + dp[child[i]][1][1], f[i - 1][1][j] + dp[child[i]][0][1]);
		}
	}
	int x = child.size() - 1;
	dp[u][0][a[u]] = f[x][0][0];
	dp[u][1][a[u]] = f[x][1][1] + 1;
	dp[u][0][a[u] ^ 1] = f[x][1][0];
	dp[u][1][a[u] ^ 1] = f[x][0][1] + 1;
}
/*
dp[u][0][a[i]] -> ko tac dong len con u
chan con dp[v][1][0] + con lai dp[v][0][0]

dp[u][0][a[i] ^ 1] -> ko tac dong len con u
le con dp[v][1][0] + con lai dp[v][0][0]

dp[u][1][a[i]] -> tac dong len con u
le con dp[v][1][1] + con lai dp[v][0][1]

dp[u][1][a[i] ^ 1] -> tac dong len con u
chan con dp[v][1][1] + con lai dp[v][0][1]
*/
signed main() {
	cin >> n;
	for (int i = 1; i < n; i++) {
		int u, v;
		cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	for (int i = 1; i <= n; i++) cin >> a[i];
	dfs(1, 1);
	int x = min(dp[1][1][0], dp[1][0][0]);
	if (x >= inf) cout << "impossible";
	else cout << x;
	return 0;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 15
• Subtask 3: 0 / 10
• Subtask 4: 0 / 40
• Subtask 5: 0 / 30