Submission #647912

#	Time	Username	Problem	Language	Result	Execution time	Memory
647912		thorie	The Xana coup (BOI21_xanadu)	C++17	20 / 100	1099 ms	12640 KiB

xanadu

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

vector<vector<int>> graph;
vector<bool> on;
vector<bool> onCopy;
vector<int> v1;
vector<int> v2;

void toggle(int k) {
    on[k] = !on[k];
    for (int i = 0; i < graph[k].size(); i++) {
        on[graph[k][i]] = !on[graph[k][i]];
    }
}

void dfs(int x, bool y, int from) {
    if (y) {
        v1.push_back(x);
    }
    else {
        v2.push_back(x);
    }
    for (int i = 0; i < graph[x].size(); i++) {
        if (graph[x][i] != from) {
            dfs(graph[x][i], !y, x);
        }
    }
}

int main() {
    int n;
    cin >> n;

    graph.resize(n);
    on.resize(n);

    for (int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;
        graph[a - 1].push_back(b - 1);
        graph[b - 1].push_back(a - 1);
    }

    for (int i = 0; i < n; i++) {
        bool a;
        cin >> a;
        on[i] = a;
    }

    onCopy = on;

    dfs(0, false, -1);

    if (v1.size() > v2.size()) {
        swap(v1, v2);
    }

    int m = INT_MAX;

    for (int i = 0; i < 1 << v1.size(); i++) {
        int cnt = 0;

        for (int j = 0; j < v1.size(); j++) {
            if (i & 1 << j) {
                toggle(v1[j]);
                cnt++;
            }
        }

        for (int j = 0; j < v2.size(); j++) {
            if (on[v2[j]]) {
                toggle(v2[j]);
                cnt++;
            }
        }

        bool allFalse = true;
        for (int j = 0; j < v1.size(); j++) {
            if (on[v1[j]]) {
                allFalse = false;
                break;
            }
        }

        if (allFalse) {
            m = min(m, cnt);
        }

        on = onCopy;
    }

    if (m == INT_MAX) {
        cout << "impossible" << endl;
    }
    else {
        cout << m << endl;
    }

    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'void toggle(int)':
xanadu.cpp:12:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |     for (int i = 0; i < graph[k].size(); i++) {
      |                     ~~^~~~~~~~~~~~~~~~~
xanadu.cpp: In function 'void dfs(int, bool, int)':
xanadu.cpp:24:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |     for (int i = 0; i < graph[x].size(); i++) {
      |                     ~~^~~~~~~~~~~~~~~~~
xanadu.cpp: In function 'int main()':
xanadu.cpp:64:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   64 |         for (int j = 0; j < v1.size(); j++) {
      |                         ~~^~~~~~~~~~~
xanadu.cpp:71:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   71 |         for (int j = 0; j < v2.size(); j++) {
      |                         ~~^~~~~~~~~~~
xanadu.cpp:79:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   79 |         for (int j = 0; j < v1.size(); j++) {
      |                         ~~^~~~~~~~~~~

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