This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <iostream>
#include <vector>
#include <array>
#include <algorithm>
using namespace std;
using ll = long long;
const ll INF = 1e8;
void solve()
{
int n;
cin >> n;
vector<vector<int>> adj(n + 1);
for (int i = 0; i + 1 < n; ++i)
{
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
vector<int> a(n);
for (int &i : a) cin >> i;
a.insert(a.begin(), 0);
vector<array<ll, 4>> dp(n + 1, {INF, INF, INF, INF});
//first bit - he, second - father
auto dfs = [&adj, &a, &dp](auto self, int v, int p) -> void
{
if (adj[v].size() == 1 && p != 0)
{
dp[v][a[v]] = 0;
dp[v][3 - a[v]] = 1;
return;
}
for (int u : adj[v])
{
if (u != p)
{
self(self, u, v);
}
}
//we don't do operation
//then parity of number of ones
//let sum = dp[u][0], d_i = dp[u][2] - dp[u][0]
//depending on parity we add to one or other mask
vector<ll> deltas;
ll sum = 0;
int cnt = 0;
for (int u : adj[v])
{
if (u != p)
{
if (dp[u][0] == INF && dp[u][2] == INF)
{
sum = -1;
break;
}
if (dp[u][0] == INF)
{
sum += dp[u][2];
++cnt;
continue;
}
sum += dp[u][0];
if (dp[u][2] != INF) deltas.push_back(dp[u][2] - dp[u][0]);
}
}
if (sum != -1)
{
sort(deltas.begin(), deltas.end(), greater<>());
cnt += a[v];
for (int i = 0; i <= deltas.size(); ++i)
{
dp[v][cnt & 1] = min(dp[v][cnt & 1], sum);
if (i != deltas.size())
{
++cnt;
sum += deltas[i];
}
}
}
//we do operation
//then parity of number of ones
//let sum = dp[u][1], d_i = dp[u][3] - dp[u][1]
//depending on parity we add to one or other mask
deltas.clear();
sum = 0;
cnt = 1;
for (int u : adj[v])
{
if (u != p)
{
if (dp[u][1] == INF && dp[u][3] == INF)
{
sum = -1;
break;
}
if (dp[u][1] == INF)
{
sum += dp[u][3];
++cnt;
continue;
}
sum += dp[u][1];
if (dp[u][3] != INF) deltas.push_back(dp[u][3] - dp[u][1]);
}
}
if (sum != -1)
{
sort(deltas.begin(), deltas.end(), greater<>());
cnt += a[v];
for (int i = 0; i <= deltas.size(); ++i)
{
dp[v][2 + (cnt & 1)] = min(dp[v][2 + (cnt & 1)], sum + 1);
if (i != deltas.size())
{
++cnt;
sum += deltas[i];
}
}
}
};
dfs(dfs, 1, 0);
if (min(dp[1][0], dp[1][2]) == INF) cout << "impossible";
else cout << min(dp[1][0], dp[1][2]);
}
/*
5
1 2
1 3
2 4
2 5
0 1 0 1 1
*/
signed main()
{
cin.tie(0)->sync_with_stdio(0);
int t = 1;
//cin >> t;
while (t--) solve();
return 0;
}
Compilation message (stderr)
xanadu.cpp: In lambda function:
xanadu.cpp:74:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
74 | for (int i = 0; i <= deltas.size(); ++i)
| ~~^~~~~~~~~~~~~~~~
xanadu.cpp:114:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
114 | for (int i = 0; i <= deltas.size(); ++i)
| ~~^~~~~~~~~~~~~~~~
xanadu.cpp: In instantiation of 'solve()::<lambda(auto:1, int, int)> [with auto:1 = solve()::<lambda(auto:1, int, int)>]':
xanadu.cpp:125:18: required from here
xanadu.cpp:74:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
74 | for (int i = 0; i <= deltas.size(); ++i)
| ~~^~~~~~~~~~~~~~~~
xanadu.cpp:77:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
77 | if (i != deltas.size())
| ~~^~~~~~~~~~~~~~~~
xanadu.cpp:114:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
114 | for (int i = 0; i <= deltas.size(); ++i)
| ~~^~~~~~~~~~~~~~~~
xanadu.cpp:117:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
117 | if (i != deltas.size())
| ~~^~~~~~~~~~~~~~~~
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