#include <bits/stdc++.h>
#define pll pair <long long, long long>
#define fi first
#define se second
using namespace std;
#define task "code"
#define all(s) s.begin(), s.end()
typedef long long ll;
const int ar = 3e5+2;
const ll mod = 998244353;
const int oo = 1e9;
int n, a, b, child[ar], dp[ar], pre[ar], suf[ar], f[ar];
vector <int> g[ar], trace, tg[ar];
void caltrace(int u, int p) {
if(trace.empty() || trace.back() != b) {
if(trace.size()) child[trace.back()] = u;
trace.push_back(u);
}
for(auto v : g[u]) if(v != p)
caltrace(v, u);
if(trace.back() != b)
trace.pop_back(), child[trace.back()] = 0;
}
void dfs(int u, int p) {
for(auto v : g[u]) if(v != p) {
dfs(v, u);
// if(u == 3) cout << v << " 3333\n";
if(v != child[u]) {
tg[u].push_back(dp[v]);
}
}
sort(all(tg[u]), greater<int>());
// if(u == 3) cout << tg.size() << '\n';
for(int i = 0; i < tg[u].size(); ++i)
dp[u] = max(dp[u], tg[u][i] + i + 1);
for(int i = 0; i < tg[u].size(); ++i)
if(dp[u] == tg[u][i] + i + 1) f[u] = i;
// cout << u << ' ' << dp[u] << '\n';
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0), cout.tie(0);
if(fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
cin >> n >> a >> b;
for(int i = 1; i < n; ++i) {
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
caltrace(a, 0);
dfs(a, 0);
if(a == b) return cout << dp[a], 0;
int m = trace.size();
// for(auto x : trace) cout << x << ' '; cout << '\n';
if(m == 2)
return cout << max(dp[a], dp[b]), 0;
pre[0] = dp[trace[0]];
for(int i = 1; i < m - 1; ++i) {
int u = trace[i - 1], v = trace[i];
int j = 0;
for(; j < tg[u].size(); ++j)
if(tg[u][j] < dp[v]) break;
if(j <= f[u]) pre[i] = max(pre[i - 1] + 1, dp[v] + j + i);
else pre[i] = max(pre[i - 1], dp[v] + j + i);
// pre[i] = min(max(pre[i - 1], dp[v]) + i, max(pre[i - 1], dp[v] + f[u] + i));
}
suf[m - 1] = dp[trace.back()];
for(int i = m - 2; i > 0; --i) {
int u = trace[i + 1], v = trace[i];
int j = 0;
for(; j < tg[u].size(); ++j)
if(tg[u][j] < dp[v]) break;
if(j <= f[u]) suf[i] = max(suf[i + 1] + 1, dp[v] + j + m - i - 1);
else suf[i] = max(suf[i + 1], dp[v] + j + m - i - 1);
// suf[i] = min(max(suf[i + 1], dp[v]) + m - i - 1, max(suf[i + 1], dp[v] + f[u] + m - i - 1));
}
// cout << '\n';
int res = oo;
for(int i = 1; i < m; ++i)
// cout << pre[i - 1] << ' ' << suf[i] << '\n',
res = min(res, max(pre[i - 1], suf[i]));
cout << res;
return 0;
}
Compilation message
torrent.cpp: In function 'void dfs(int, int)':
torrent.cpp:40:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
40 | for(int i = 0; i < tg[u].size(); ++i)
| ~~^~~~~~~~~~~~~~
torrent.cpp:42:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
42 | for(int i = 0; i < tg[u].size(); ++i)
| ~~^~~~~~~~~~~~~~
torrent.cpp: In function 'int main()':
torrent.cpp:74:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
74 | for(; j < tg[u].size(); ++j)
| ~~^~~~~~~~~~~~~~
torrent.cpp:85:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
85 | for(; j < tg[u].size(); ++j)
| ~~^~~~~~~~~~~~~~
torrent.cpp:51:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
51 | freopen(task".inp", "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:52:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
52 | freopen(task".out", "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Incorrect |
5 ms |
16984 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Incorrect |
93 ms |
33520 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
