제출 #424144

#제출 시각아이디문제언어결과실행 시간메모리
424144dolphingarlicThe Xana coup (BOI21_xanadu)C++14
30 / 100
85 ms19736 KiB
#include <bits/stdc++.h> typedef long long ll; using namespace std; const int INF = 1e9; vector<int> graph[100001]; bool white[100001]; int dp[100001][2][2]; void dfs(int node = 1, int parent = 0) { int case_1 = 0, case_2 = 0; int switch_1 = INF, switch_2 = INF; bool parity_1 = !white[node], parity_2 = white[node]; for (int i : graph[node]) if (i != parent) { dfs(i, node); // Case 1: We switch node if (dp[i][1][0] < dp[i][1][1]) { case_1 += dp[i][1][0]; switch_1 = min(switch_1, dp[i][1][1] - dp[i][1][0]); } else { case_1 += dp[i][1][1]; switch_1 = min(switch_1, dp[i][1][0] - dp[i][1][1]); parity_1 ^= true; } // Case 2: We don't switch node if (dp[i][0][0] < dp[i][0][1]) { case_2 += dp[i][0][0]; switch_2 = min(switch_2, dp[i][0][1] - dp[i][0][0]); } else { case_2 += dp[i][0][1]; switch_2 = min(switch_2, dp[i][0][0] - dp[i][0][1]); parity_2 ^= true; } } dp[node][parity_1][1] = case_1 + 1; dp[node][!parity_1][1] = dp[node][parity_1][1] + switch_1; dp[node][parity_2][0] = case_2; dp[node][!parity_2][0] = dp[node][parity_2][0] + switch_2; } int main() { cin.tie(0)->sync_with_stdio(0); int n; cin >> n; for (int i = 1; i < n; i++) { int u, v; cin >> u >> v; graph[u].push_back(v); graph[v].push_back(u); } for (int i = 1; i <= n; i++) cin >> white[i]; dfs(); int ans = min(dp[1][0][0], dp[1][0][1]); if (ans > n) cout << "impossible"; else cout << ans; return 0; }
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