Submission #444249

#	Time	Username	Problem	Language	Result	Execution time	Memory
444249		parsabahrami	The Xana coup (BOI21_xanadu)	C++17	100 / 100	139 ms	36644 KiB

xanadu

/* I do it for the glory */
#include <bits/stdc++.h>
 
using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
 
#define SZ(x)                       (int) x.size()
#define F                           first
#define S                           second

const int N = 1e6 + 10, MOD = 1e9 + 7;
int n, C[N]; vector<int> adj[N]; ll dp[2][2][N]; // [root ro zadim ya na][root akharesh chie][root] :clown:

void DFS(int v, int p = -1) {
    if (SZ(adj[v]) < 2 && v > 1) {
        dp[0][C[v]][v] = 0;
        dp[0][C[v] ^ 1][v] = dp[1][C[v]][v] = MOD;
        dp[1][!C[v]][v] = 1;
        return;
    }
    for (int &u : adj[v])   
        if (u != p) DFS(u, v);
    ll c = 0, m = MOD;
    for (int &u : adj[v]) {
        if (u != p) {
            if (dp[1][0][u] <= dp[0][0][u]) 
                c++;
            m = min(m, abs(dp[1][0][u] - dp[0][0][u]));
        }
    }
    for (int &u : adj[v]) {
        if (u != p) {
            dp[0][(c & 1) ^ C[v]][v] += min(dp[1][0][u], dp[0][0][u]);
        }
    }
    dp[0][(c & 1) ^ C[v] ^ 1][v] = dp[0][(c & 1) ^ C[v]][v] + m;
    c = 0, m = MOD;
    for (int &u : adj[v]) {
        if (u != p) {
            if (dp[1][1][u] <= dp[0][1][u]) 
                c++;
            m = min(m, abs(dp[1][1][u] - dp[0][1][u]));
        }
    }
    for (int &u : adj[v]) {
        if (u != p) {
            dp[1][(c & 1) ^ C[v] ^ 1][v] += min(dp[1][1][u], dp[0][1][u]);
        }
    }
    dp[1][(c & 1) ^ C[v] ^ 1][v]++;
    dp[1][(c & 1) ^ C[v]][v] = dp[1][(c & 1) ^ C[v] ^ 1][v] + m;
}

int main() {
    scanf("%d", &n);
    for (int i = 1; i < n; i++) {
        int u, v; scanf("%d%d", &u, &v);
        adj[u].push_back(v);
        adj[v].push_back(u);
    }    
    for (int i = 1; i <= n; i++) 
        scanf("%d", &C[i]);
    DFS(1);
    printf(min(dp[1][0][1], dp[0][0][1]) > n ? "impossible\n" : "%lld\n", min(dp[1][0][1], dp[0][0][1]));
    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'int main()':
xanadu.cpp:57:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   57 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
xanadu.cpp:59:24: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   59 |         int u, v; scanf("%d%d", &u, &v);
      |                   ~~~~~^~~~~~~~~~~~~~~~
xanadu.cpp:64:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   64 |         scanf("%d", &C[i]);
      |         ~~~~~^~~~~~~~~~~~~

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