Submission #447300

#	Time	Username	Problem	Language	Result	Execution time	Memory
447300		blue	The Xana coup (BOI21_xanadu)	C++17	100 / 100	181 ms	30072 KiB

xanadu

#include <iostream>
#include <vector>
using namespace std;
#define FOR(i,n) for(int i = 1; i <= N; i++)
vector<int> edge[100001];
int sv[100001];
vector<int> p(100001, 0);
vector<int> children[100001];
int** dp[100001];
void dfs1(int u) {
    for(int v: edge[u]) {
        if(p[u] == v) continue;
        p[v] = u;
        children[u].push_back(v);
        dfs1(v);
    }
}
int** X;
void dfs2(int u) {
    dp[u][ sv[u] ][0] = dp[u][ sv[u] ][1] = 0;
    for(int v: children[u]) {
        dfs2(v);
        for(int f = 0; f <= 1; f++) for(int g = 0; g <= 1; g++) X[f][g] = min(dp[u][f][g] + dp[v][g][0], dp[u][!f][g] + dp[v][!g][1] + 1);
        swap(dp[u], X);
    }
}
int main() {
    X = new int*[2];
    for(int f = 0; f < 2; f++)  X[f] = new int[2];
    int N; cin >> N;
    for(int i = 1; i <= N-1; i++) {
        int a, b; cin >> a >> b;
        edge[a].push_back(b);
        edge[b].push_back(a);
    }
    edge[1].push_back(0);
    edge[0].push_back(1);
    dfs1(0);
    for(int i = 0; i <= N; i++) {
        dp[i] = new int*[2];
        for(int f = 0; f <= 1; f++)
        {
            dp[i][f] = new int[2];
            for(int g = 0; g <= 1; g++) dp[i][f][g] = N+1;
        }
    }
    FOR(i, N) cin >> sv[i];
    dp[0][0][0] = dp[0][0][1] = dp[0][1][0] = dp[0][1][1] = 0;
    dfs2(0);
    int res = min(dp[0][0][0], dp[0][1][0]);
    if(res >= N+1) cout << "impossible\n";
    else cout << res << '\n';
}

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