Submission #683116

#	Time	Username	Problem	Language	Result	Execution time	Memory
683116		BhavayGoyal	The Xana coup (BOI21_xanadu)	C++14	100 / 100	147 ms	30932 KiB

xanadu

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

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

template<class T> using oset = 
            tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define ll long long
#define ld long double
#define ar array
#define vi vector<int>
#define vii vector<vector<int>>     
#define pii pair<int, int>
#define pb push_back
#define all(x) x.begin(), x.end()
#define f first
#define s second
#define endl "\n"

const int MOD = 1e9+7;
const int inf = 1e9;
const ll linf = 1e18;

const int d4i[4]={-1, 0, 1, 0}, d4j[4]={0, 1, 0, -1};
const int d8i[8]={-1, -1, 0, 1, 1, 1, 0, -1}, d8j[8]={0, 1, 1, 1, 0, -1, -1, -1};


// -------------------------------------------------- Main Code --------------------------------------------------

const int N = 1e5+5;
int n, initial[N];
vi g[N];

int memo[N][2][2];

int sol(int idx, int sum, vector<array<int, 2>> &child, int reqSum, vii &dp) {
    if (idx == child.size()) {
        if (sum == reqSum) return 0;
        return n+1;
    }
    if (dp[idx][sum] != -1) return dp[idx][sum];
    int ans = sol(idx+1, sum, child, reqSum, dp) + child[idx][0];
    ans = min(ans, sol(idx+1, (sum+1)%2, child, reqSum, dp) + child[idx][1]);
    return dp[idx][sum] = ans;
}

int dfs(int src, int par, int lastSwitched, int currSwitched) {
    if (memo[src][lastSwitched][currSwitched] != -1) return memo[src][lastSwitched][currSwitched];
    vector<array<int, 2>> child; // child[i][0] = childNotSwitched else childSwitched
    for (auto ch : g[src]) {
        if (ch == par) continue;
        child.pb({dfs(ch, src, currSwitched, false), 1+dfs(ch, src, currSwitched, true)});
    }

    int x = (initial[src] + lastSwitched + currSwitched)%2;
    vii dp(child.size()+1, vi(2, -1));
    return memo[src][lastSwitched][currSwitched] = sol(0, 0, child, x, dp);
}

void sol() {
    cin >> n;
    for (int i = 0; i < n-1; i++) {
        int a, b; cin >> a >> b;
        --a; --b;
        g[a].pb(b);
        g[b].pb(a);
    }
    for (int i = 0; i < n; i++) cin >> initial[i];

    memset(memo, -1, sizeof memo);

    int ans = min(dfs(0, -1, 0, 0), 1+dfs(0, -1, 0, 1));
    if (ans > n) cout << "impossible" << endl;
    else cout << ans << endl;
}

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t = 1;
    // cin >> t;
    while (t--) {
        sol();
    }
    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'int sol(int, int, std::vector<std::array<int, 2> >&, int, std::vector<std::vector<int> >&)':
xanadu.cpp:40:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 2> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |     if (idx == child.size()) {
      |         ~~~~^~~~~~~~~~~~~~~

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