Submission #391529

#	Time	Username	Problem	Language	Result	Execution time	Memory
391529		Killer2501	Torrent (COI16_torrent)	C++14	100 / 100	136 ms	38996 KiB

torrent

#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define task "asd"
#define pll pair<ll, ll>
#define pii pair<pll, ll>
#define fi first
#define se second

using namespace std;
const ll mod = 3;
const ll N = 4e5+5;
const int base = 313;
ll n, k, m, tong, ans, t, a[N], b[N], d[N], s;
ll pw(ll k, ll n)
{
    ll total = 1;
    for(; n; n >>= 1)
    {
        if(n & 1)total = total * k % mod;
        k = k * k % mod;
    }
    return total;
}
vector<ll> kq, adj[N];
void add(ll id, ll val)
{
    for(; id <= n; id += id & -id)b[id] = max(b[id], val);
}
ll get(ll id)
{
    ll total = 0;
    for(; id; id -= id & -id)total = max(total, b[id]);
    return total;
}
struct node
{
    ll A, B, C, sl;
}p[N];
ll A, B;
void dfs(ll u, ll p)
{
    vector<ll> val;
    for(ll v : adj[u])
    {
        if(v == p)continue;
        dfs(v, u);
        b[u] |= b[v];
        if(b[v])continue;
        val.pb(a[v]+1);
    }
    if(u == B)b[u] = 1;
    if(b[u])kq.pb(u);
    sort(val.rbegin(), val.rend());
    for(int i = 0; i < val.size(); i ++)a[u] = max(a[u], val[i] + i);
}
bool check(ll mid)
{
    fill_n(d, n+2, 0);
    ll cur = 0;
    for(ll x : kq)
    {
        if(a[x] + cur + 1 <= mid)d[x] = 1, ++cur;
        else if(a[x] + cur <= mid)cur += 2, d[x] = 1;
        else cur += 2;
    }
    cur = 0;
    for(int i = kq.size()-1; i >= 0; i --)
    {
        ll x = kq[i];
        if(a[x] + cur + 1 <= mid)d[x] = 1, ++cur;
        else if(a[x] + cur <= mid)cur += 2, d[x] = 1;
        else cur += 2;
        if(d[x] == 0)return false;
    }
    return true;
}
void sol()
{
    cin >> n >> A >> B;
    for(int i = 1; i < n; i ++)
    {
        ll x ,y;
        cin >> x >> y;
        adj[x].pb(y);
        adj[y].pb(x);
    }
    dfs(A, 0);
    ll lf = 0, rt = n, mid;
    while(lf <= rt)
    {
        mid = (lf + rt) / 2;
        if(check(mid))rt = mid - 1;
        else lf = mid + 1;
    }
    cout << lf;
}
int main()
{
    if(fopen(task".INP", "r"))
    {
       freopen(task".INP", "r", stdin);
       freopen(task".OUT", "w", stdout);
    }
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int ntest = 1;
    //cin >> ntest;
    while(ntest -- > 0)
    sol();
}
/*
6
BWWRBW
4
WWRB
https://codeforces.com/contest/791/problem/E

*/

Compilation message (stderr)

torrent.cpp: In function 'void dfs(long long int, long long int)':
torrent.cpp:55:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   55 |     for(int i = 0; i < val.size(); i ++)a[u] = max(a[u], val[i] + i);
      |                    ~~^~~~~~~~~~~~
torrent.cpp: In function 'int main()':
torrent.cpp:102:15: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  102 |        freopen(task".INP", "r", stdin);
      |        ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:103:15: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  103 |        freopen(task".OUT", "w", stdout);
      |        ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 31 / 31
• Subtask 2: 69 / 69