Submission #415208

#	Time	Username	Problem	Language	Result	Execution time	Memory
415208		tengiz05	The Xana coup (BOI21_xanadu)	C++17	100 / 100	154 ms	39368 KiB

xanadu

#include <bits/stdc++.h>
using i64 = long long;
constexpr int N = 1e5;
i64 dp[N][2][2], a[N];
std::vector<int> e[N];
struct opt{
    std::vector<i64> pr;
    i64 sum;
    opt(std::vector<i64> a, std::vector<i64> b) : pr(a.size() + 1), sum(0) {
        std::vector<i64> v;
        for (int i = 0; i < int(a.size()); i++) {
            v.push_back(-a[i] + b[i]);
        }
        sort(v.begin(), v.end());
        for (int i = 0; i < int(v.size()); i++) {
            sum += a[i];
            pr[i + 1] = pr[i] + v[i];
        }
    }
    i64 odd() {
        i64 res = 1e9;
        for (int i = 1; i < pr.size(); i += 2) {
            res = std::min(res, pr[i] + sum);
        }
        return res;
    }
    i64 even() {
        i64 res = 1e9;
        for (int i = 0; i < pr.size(); i += 2) {
            res = std::min(res, pr[i] + sum);
        }
        return res;
    }
};
void dfs(int u, int p) {
    if (e[u].size() == 1 && p != -1) {
        if (a[u] == 0) {
            dp[u][0][0] = 0;
            dp[u][1][1] = 1;
        } else {
            dp[u][1][0] = 0;
            dp[u][0][1] = 1;
        }
        return;
    }
    std::vector<int> c;
    for (auto v : e[u]) {
        if (v == p) continue;
        dfs(v, u);
        c.push_back(v);
    }
    int k = c.size();
    if (k == 1) {
        int l = c[0];
        if (a[u] == 0) {
            dp[u][0][0] = dp[l][0][0];
            dp[u][0][1] = dp[l][1][1] + 1;
            dp[u][1][0] = dp[l][0][1];
            dp[u][1][1] = dp[l][1][0] + 1;
        } else {
            dp[u][1][0] = dp[l][0][0];
            dp[u][1][1] = dp[l][1][1] + 1;
            dp[u][0][0] = dp[l][0][1];
            dp[u][0][1] = dp[l][1][0] + 1;
        }
    } else {
        if (a[u] == 0) {
            {
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][0][0]);
                for (auto x : c) B.push_back(dp[x][0][1]);
                opt p(A, B);
                dp[u][0][0] = p.even();
            }{
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][1][0]);
                for (auto x : c) B.push_back(dp[x][1][1]);
                opt p(A, B);
                dp[u][0][1] = p.odd() + 1;
            }
            {
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][0][0]);
                for (auto x : c) B.push_back(dp[x][0][1]);
                opt p(A, B);
                dp[u][1][0] = p.odd();
            }{
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][1][0]);
                for (auto x : c) B.push_back(dp[x][1][1]);
                opt p(A, B);
                dp[u][1][1] = p.even() + 1;
            }
        } else {
            {
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][0][0]);
                for (auto x : c) B.push_back(dp[x][0][1]);
                opt p(A, B);
                dp[u][1][0] = p.even();
            }{
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][1][0]);
                for (auto x : c) B.push_back(dp[x][1][1]);
                opt p(A, B);
                dp[u][1][1] = p.odd() + 1;
            }
            {
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][0][0]);
                for (auto x : c) B.push_back(dp[x][0][1]);
                opt p(A, B);
                dp[u][0][0] = p.odd();
            }{
                std::vector<i64> A, B;
                for (auto x : c) A.push_back(dp[x][1][0]);
                for (auto x : c) B.push_back(dp[x][1][1]);
                opt p(A, B);
                dp[u][0][1] = p.even() + 1;
            }
        }
    }
}
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int n;
    std::cin >> n;
    for (int i = 0; i < n - 1; i++) {
        int u, v;
        std::cin >> u >> v;
        u--;
        v--;
        e[u].push_back(v);
        e[v].push_back(u);
    }
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
    }
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < 2; j++) {
            for (int k = 0; k < 2; k++) {
                dp[i][j][k] = 1e9;
            }
        }
    }
    dfs(0, -1);
    i64 ans = 1e9;
    for (int j = 0; j < 2; j++) {
        ans = std::min(ans, dp[0][0][j]);
    }
    if (ans == 1e9) {
        std::cout << "impossible\n";
    } else {
        std::cout << ans << "\n";
    }
    return 0;
}

Compilation message (stderr)

xanadu.cpp: In member function 'i64 opt::odd()':
xanadu.cpp:22:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |         for (int i = 1; i < pr.size(); i += 2) {
      |                         ~~^~~~~~~~~~~
xanadu.cpp: In member function 'i64 opt::even()':
xanadu.cpp:29:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |         for (int i = 0; i < pr.size(); i += 2) {
      |                         ~~^~~~~~~~~~~

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