Submission #328532

#	Time	Username	Problem	Language	Result	Execution time	Memory
328532		Falcon	Torrent (COI16_torrent)	C++17	100 / 100	732 ms	25428 KiB

torrent

#pragma GCC optimize("O2")

#include <bits/stdc++.h>

#ifdef DEBUG
#include "debug.hpp"
#endif

using namespace std;

#define all(c)              (c).begin(), (c).end()
#define rall(c)             (c).rbegin(), (c).rend()
#define traverse(c, it)     for(auto it = (c).begin(); it != (c).end(); ++it)
#define rep(i, N)           for(int i = 0; i < (N); ++i)
#define rrep(i, N)          for(int i = (N) - 1; i >= 0; --i)
#define rep1(i, N)          for(int i = 1; i <= (N); ++i)
#define rep2(i, s, e)       for(int i = (s); i <= (e); ++i)
#define rep3(i, s, e, d)    for(int i = (s); (d) >= 0 ? i <= (e) : i >= (e); i += (d))
#define pb push_back

#ifdef DEBUG
#define debug(x...) {       ++dbg::depth; \
                            string dbg_vals = dbg::to_string(x); \
                            --dbg::depth; \
                            dbg::fprint(__func__, __LINE__, #x, dbg_vals); }

#define light_debug(x) {    dbg::light = 1; \
                            dbg::dout << __func__ << ":" << __LINE__ << "  " \
                                << #x << " = " << x << endl; \
                            dbg::light = 0; }
#else
#define debug(x...)         42
#define light_debug(x)      42
#endif


using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

template<typename T>
inline T& ckmin(T& a, T b) { return a = a > b ? b : a; }

template<typename T>
inline T& ckmax(T& a, T b) { return a = a < b ? b : a; }


template<class Fun>
class y_combinator_result {
    Fun fun_;
public:
    template<class T>
    explicit y_combinator_result(T &&fun): fun_(std::forward<T>(fun)) {}

    template<class ...Args>
    decltype(auto) operator()(Args &&...args) {
        return fun_(std::ref(*this), std::forward<Args>(args)...);
    }
};

template<class Fun>
decltype(auto) y_combinator(Fun &&fun) {
    return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
}


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    
    #ifdef DEBUG
    freopen("debug", "w", stderr);
    #endif

    int n, a, b; cin >> n >> a >> b; --a, --b;
    vector<vector<int>> adj(n);
    rep(_, n - 1) {
        int u, v; cin >> u >> v; --u, --v;
        adj[u].pb(v), adj[v].pb(u);
    }
    debug(adj);

    auto solve_for = [&](int r) {
        return y_combinator([&](auto rec, int u, int p) -> int {
                    vector<int> s; s.reserve(adj[u].size());                
                    for(int v : adj[u])
                        if(v != p)
                            s.pb(rec(v, u));

                    sort(rall(s));   
                    int res = 0;
                    rep(i, int(s.size())) 
                        ckmax(res, s[i] += i + 1);
                    return res;
                })(r, -1);
    };
    
    auto get_path = [&](int s, int e) {
        vector<int> parent(n);
        y_combinator([&](auto dfs, int u, int p) -> void {
                    parent[u] = p;
                    for(int v : adj[u])
                        if(v != p)
                            dfs(v, u);
                })(s, -1);
        vector<int> path;
        for(int t = e; ~t; t = parent[t])
            path.pb(t);
        reverse(all(path));
        return path;
    };

    vector<int> path = get_path(a, b);
    vector<int> ans(int(path.size()) - 1, 1 << 27);

    debug(path);

    auto check = [&](int i) {
        assert(i >= 0 && i + 1 < int(path.size()));
        int x = path[i], y = path[i + 1];
        adj[x].erase(find(all(adj[x]), y));
        adj[y].erase(find(all(adj[y]), x));

        int t_a =  solve_for(a), t_b = solve_for(b);
        ans[i] = max(t_a, t_b);

        adj[x].pb(y);
        adj[y].pb(x);
        return t_a - t_b;
    };
    
    int j{-1};
    for(int k = 1 << __lg(int(path.size())); k > 0; k >>= 1)
        if(int i = j + k; i + 1 < int(path.size()) && check(i) < 0)
            j = i;
    
    if(j + 1  < int(path.size()))
        check(j + 1);

    cout << *min_element(all(ans)) << '\n';


    #ifdef DEBUG
    dbg::dout << "\nExecution time: " << clock() << "ms\n";
    #endif

    return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'int main()':
torrent.cpp:32:29: warning: statement has no effect [-Wunused-value]
   32 | #define debug(x...)         42
      |                             ^~
torrent.cpp:81:5: note: in expansion of macro 'debug'
   81 |     debug(adj);
      |     ^~~~~
torrent.cpp:32:29: warning: statement has no effect [-Wunused-value]
   32 | #define debug(x...)         42
      |                             ^~
torrent.cpp:116:5: note: in expansion of macro 'debug'
  116 |     debug(path);
      |     ^~~~~

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