Submission #601218

#	Time	Username	Problem	Language	Result	Execution time	Memory
601218		maomao90	The Xana coup (BOI21_xanadu)	C++17	100 / 100	80 ms	16560 KiB

xanadu

// Hallelujah, praise the one who set me free
// Hallelujah, death has lost its grip on me
// You have broken every chain, There's salvation in your name
// Jesus Christ, my living hope
#include <bits/stdc++.h> 
using namespace std;

#define REP(i, s, e) for (int i = (s); i < (e); i++)
#define RREP(i, s, e) for (int i = (s); i >= (e); i--)
template <class T>
inline bool mnto(T& a, T b) {return a > b ? a = b, 1 : 0;}
template <class T>
inline bool mxto(T& a, T b) {return a < b ? a = b, 1: 0;}
typedef long long ll;
typedef long double ld;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> iii;
#define ALL(_a) _a.begin(), _a.end()
#define SZ(_a) (int) _a.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
typedef vector<iii> viii;

#ifndef DEBUG
#define cerr if (0) cerr
#endif

const int INF = 1000000005;
const ll LINF = 1000000000000000005ll;
const int MAXN = 100005;

int n;
vi adj[MAXN];
bool a[MAXN];

int dp[MAXN][2][2];
void dfs(int u, int p) {
    bool rt = 1;
    for (int v : adj[u]) {
        if (v == p) {
            continue;
        }
        rt = 0;
        dfs(v, u);
    }
    if (rt) {
        REP (x, 0, 2) {
            REP (y, 0, 2) {
                dp[u][x][y] = INF;
            }
        }
        REP (x, 0, 2) {
            dp[u][x][a[u] ^ x] = x;
        }
        return;
    }
    REP (x, 0, 2) { // x = whether self is pressed
        int y = a[u] ^ x;
        int sm = x;
        for (int v : adj[u]) {
            if (v == p) {
                continue;
            }
            if (dp[v][0][x] < dp[v][1][x]) {
                sm += dp[v][0][x];
                mnto(sm, INF);
            } else {
                sm += dp[v][1][x];
                mnto(sm, INF);
                y ^= 1;
            }
        }
        dp[u][x][y] = sm;
        int mn = INF;
        for (int v : adj[u]) {
            if (v == p) {
                continue;
            }
            mnto(mn, abs(dp[v][0][x] - dp[v][1][x]));
        }
        dp[u][x][y ^ 1] = min(sm + mn, INF);
    }
}

int main() {
#ifndef DEBUG
    ios::sync_with_stdio(0), cin.tie(0);
#endif
    cin >> n;
    REP (i, 1, n) {
        int u, v; cin >> u >> v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    REP (i, 1, n + 1) {
        cin >> a[i];
    }
    dfs(1, -1);
    int ans = INF;
    REP (x, 0, 2) {
        mnto(ans, dp[1][x][0]);
    }
    if (ans == INF) {
        cout << "impossible\n";
    } else {
        cout << ans << '\n';
    }
    return 0;
}

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