#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define ll long long
#define mp(x, y) make_pair(x, y)
#define sz(v) ((int) (v).size())
#define all(v) (v).begin(), (v).end()
#define MASK(i) (1LL << (i))
#define BIT(x, y) (((x) >> (y)) & 1)
#define pb push_back
#define max_rng *max_element
#define min_rng *min_element
#define rep(i, n) for(int i = 1, _n = (n); i <= _n; ++i)
#define forn(i, a, b) for(int i = (a), _b = (b); i <= _b; ++i)
#define ford(i, a, b) for(int i = (a), _b = (b); i >= _b; --i)
template <class X, class Y>
inline bool maximize(X &x, Y y) {
return (x < y ? x = y, true : false);
}
template <class X, class Y>
inline bool minimize(X &x, Y y) {
return (x > y ? x = y, true : false);
}
template <class X>
inline void compress(vector<X> &a) {
sort(all(a));
a.resize(unique(all(a)) - a.begin());
}
int ctz(ll x) { return __builtin_ctzll(x); }
int lg(ll x) { return 63 - __builtin_clzll(x); }
int popcount(ll x) { return __builtin_popcount(x); }
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rand(ll l, ll r) {
return l + abs((ll) rng()) % (r - l + 1);
}
const ll oo = (ll) 1e17;
const int inf = (ll) 2e9 + 7, mod = (ll) 1e9 + 7;
const int mxn = 3e5 + 5, mxm = 3e2 + 5;
const int LG = 18, BASE = 311;
void add(int &x, int y) { x += y; if (x >= mod) x -= mod; }
void sub(int &x, int y) { x -= y; if (x < 0) x += mod; }
int n, a, b;
vector<int> g[mxn];
int par[mxn];
void calc(int u, int p) {
par[u] = p;
for (int v : g[u]) if (v != p)
calc(v, u);
return;
}
vector<pair<int, int>> road;
vector<int> g1[mxn], g2[mxn];
void build(int u, int p, int ban, int t) {
for (int v : g[u]) if (v != p && v != ban) {
build(v, u, ban, t);
if (t == 1) {
g1[v].pb(u);
g1[u].pb(v);
}
else {
g2[v].pb(u);
g2[u].pb(v);
}
}
}
int f[4][mxn];
void dfs(int u, int p, int t) {
const vector<int> &adj = (t == 1 ? g1[u] : g2[u]);
vector<int> lst;
for (int v : adj) if (v != p) {
dfs(v, u, t);
lst.pb(f[t][v]);
}
sort(all(lst));
reverse(all(lst));
rep(i, sz(lst)) {
maximize(f[t][u], lst[i-1] + i);
}
return;
}
pair<int, int> solve(int pos) {
build(a, 0, road[pos].fi, 1);
build(b, 0, road[pos].se, 2);
rep(i, 2) memset(f[i], 0, sizeof f[i]);
dfs(a, 0, 1); dfs(b, 0, 2);
rep(i, n) {
g1[i].clear();
g2[i].clear();
}
return mp(f[1][a], f[2][b]);
}
int main(void) {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#define TASK "task"
if (fopen(TASK".inp", "r")) {
freopen(TASK".inp", "r", stdin);
freopen(TASK".out", "w", stdout);
}
cin >> n >> a >> b;
rep(i, n - 1) {
int u, v;
cin >> u >> v;
g[u].pb(v);
g[v].pb(u);
}
calc(a, 0);
for (int p = b; p && p != a; p = par[p]) {
road.pb(mp(p, par[p]));
}
int ans = inf;
for(int l = 0, r = sz(road) - 1; l <= r; ) {
int m = (l + r) >> 1;
pair<int, int> res = solve(m);
if (res.fi >= res.se) {
l = m + 1;
}
else r = m - 1;
minimize(ans, max(res.fi, res.se));
}
cout << ans;
return 0;
}
Compilation message
torrent.cpp: In function 'int main()':
torrent.cpp:120:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
120 | freopen(TASK".inp", "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:121:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
121 | freopen(TASK".out", "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
12 ms |
23896 KB |
Output is correct |
| 2 |
Correct |
12 ms |
23900 KB |
Output is correct |
| 3 |
Correct |
12 ms |
23900 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
431 ms |
53520 KB |
Output is correct |
| 2 |
Correct |
452 ms |
55040 KB |
Output is correct |
| 3 |
Correct |
395 ms |
56700 KB |
Output is correct |
| 4 |
Correct |
402 ms |
55244 KB |
Output is correct |
| 5 |
Correct |
364 ms |
52816 KB |
Output is correct |
| 6 |
Correct |
346 ms |
53160 KB |
Output is correct |
| 7 |
Correct |
353 ms |
56808 KB |
Output is correct |
