Submission #1022069

#	Time	Username	Problem	Language	Result	Execution time	Memory
1022069		harzuqi	The Xana coup (BOI21_xanadu)	C++14	100 / 100	52 ms	19948 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;

#define ll long long

const int X = 3e5 + 5;

int n, dp[X][2][2];
vector<int> adj[X];
bool vis[X], kondisi[X];

void dfs(int cur) {
    vis[cur] = 1;
    if(kondisi[cur]) {
        dp[cur][1][0] = 1;
        dp[cur][0][1] = 0;
    } else {
        dp[cur][0][0] = 0;
        dp[cur][1][1] = 1;
    }
    for(int nxt: adj[cur]) {
        if(vis[nxt]) continue;
        dfs(nxt);
        // no toggle
        int prev_no = dp[cur][0][0], prev_yes = dp[cur][0][1];
        // off
        dp[cur][0][0] = min(dp[nxt][0][0] + prev_no, dp[nxt][1][0] + prev_yes);
        // on
        dp[cur][0][1] = min(dp[nxt][0][0] + prev_yes, dp[nxt][1][0] + prev_no);
        // toggle
        prev_no = dp[cur][1][0], prev_yes = dp[cur][1][1]; 
        dp[cur][1][0] = min(dp[nxt][0][1] + prev_no, dp[nxt][1][1] + prev_yes);
        dp[cur][1][1] = min(dp[nxt][0][1] + prev_yes, dp[nxt][1][1] + prev_no); 
    }
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    
    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 >> kondisi[i];
    for(int i = 1; i <= n; i++) {
        for(int j = 0; j < 2; j++) {
            for(int k = 0; k < 2; k++) {
                dp[i][j][k] = 1e6;
            }
        }
    }

    dfs(1);
    if(min(dp[1][1][0], dp[1][0][0]) > n) {
        cout << "impossible" << endl;
    } else cout << min(dp[1][1][0], dp[1][0][0]) << endl;

    return 0;
}

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