Submission #1119144

#	Time	Username	Problem	Language	Result	Execution time	Memory
1119144		quochuy147	Torrent (COI16_torrent)	C++14	100 / 100	460 ms	54540 KiB

torrent

#include <bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define ll long long
#define mp make_pair
#define pb push_back
#define pii pair<int, int>
#define pll pair<ll, ll>
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
#define all(x) (x).begin() , (x).end()
#define TIME  (1.0 * clock() / CLOCKS_PER_SEC)
#define file "name"
template <typename T1, typename T2> bool minimize(T1 &a, T2 b){if (a > b) {a = b; return true;} return false;}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b){if (a < b) {a = b; return true;} return false;}

const int inf = 1e9;
const ll linf = 1e17;
const int mod = 1e9 + 7;
const int N = 1e6 + 5;

int n, s, t;
int en[2][N];
vector <int> a[N];
vector <int> p;
bool check;
int res = inf;
int f[N];

void inp()
{
    cin >> n >> s >> t;
    for(int i = 1; i < n; ++i) {
        int u, v;
        cin >> u >> v;
        a[u].pb(v);
        a[v].pb(u);
    }
}

void dfs_pre(int u, int pre) {
    if(u == t) check = 1;
    for(int v : a[u]) {
        if(v == pre || check) continue;
        dfs_pre(v, u);
    }
    if(check) p.pb(u);
}

int dfs(int u, int pre, bool type) {
    f[u] = 0;
    vector <int> x;
    for(int v : a[u]) {
        if(v == pre || en[type][v]) continue;
        x.pb(dfs(v, u, type));
    }
    sort(x.begin(), x.end(), greater <int>());
    for(int i = 0; i < x.size(); ++i) maximize(f[u], x[i] + i + 1);
    return f[u];
}

bool cal(int k) {
    en[1][p[k]] = 1;
    en[0][p[k + 1]] = 1;
    int cx = dfs(s, 0, 0);
    int cy = dfs(t, 0, 1);
//    cout << cx << ' ' << cy << '\n';
    minimize(res, max(cx, cy));
    en[1][p[k]] = 0;
    en[0][p[k + 1]] = 0;
    return cx <= cy;
}

void solve()
{
    dfs_pre(s, s);
    reverse(p.begin(), p.end());
    cal(0);
    int l = 0, r = p.size() - 2, id = 1;
    while(l <= r) {
        int m = (l + r) >> 1;
        if(cal(m)) {
            l = m + 1;
            id = m;
        }
        else r = m - 1;
    }
    if(id + 1 < p.size()) cal(id + 1);
    cout << res;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
//    freopen(file".inp" , "r" , stdin);
//    freopen(file".out" , "w" , stdout);
    inp();
    solve();
    return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'int dfs(int, int, bool)':
torrent.cpp:61:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   61 |     for(int i = 0; i < x.size(); ++i) maximize(f[u], x[i] + i + 1);
      |                    ~~^~~~~~~~~~
torrent.cpp: In function 'void solve()':
torrent.cpp:91:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   91 |     if(id + 1 < p.size()) cal(id + 1);
      |        ~~~~~~~^~~~~~~~~~

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