Submission #640963

#	Time	Username	Problem	Language	Result	Execution time	Memory
640963		Ez0zIOVgTsSgT	Torrent (COI16_torrent)	C++14	100 / 100	406 ms	28448 KiB

torrent

#include<bits/stdc++.h>
using namespace std;

void DBG() { cerr << "]\n"; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << h; if(sizeof...(t)) cerr << ", ";
    DBG(t...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif // LOCAL

#define FOR(i,a,b) for(int i = (a) ; i<(b) ; i++)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for(int i = (b)-1 ; i>=(a) ; i--)
#define R0F(i,a) ROF(i,0,a)
#define each(e,a) for(auto &e : (a))
#define sz(v) (int)(v).size()
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define pb push_back
#define tcT template<class T
#define nl "\n"

using ll = long long;
using vi = vector<int>;
using pi = pair<int,int>;
using str = string;
tcT> using V = vector<T>;
tcT> using pqg = priority_queue<T,vector<T>,greater<T>>;

void setIO(string NAME = "") {
    cin.tie(0)->sync_with_stdio(0);
    if(sz(NAME)) {
        freopen((NAME + ".inp").c_str(),"r",stdin);
        freopen((NAME + ".out").c_str(),"w",stdout);
    }
}

tcT> bool ckmin(T&a, const T&b) {
    return b < a ? a=b,1 : 0; }
tcT> bool ckmax(T&a, const T&b) {
    return b > a ? a=b,1 : 0; }

const int MOD = 1e9 + 7;

const int MX = 3e5+5;
int N, A, B;
vi adj[MX];
vi tmp, pathAB;
int dp[MX];

void dfs(int u, int p) {
    tmp.pb(u);
    if(u == B) {
        pathAB = tmp;
        return;
    }
    each(v, adj[u]) if(v != p) {
        dfs(v, u);
    }
    tmp.pop_back();
}

int calc(int u, int p, int blk) {
    dp[u] = 0;
    if(u == blk) return dp[u];
    vi vals;
    each(v, adj[u]) if(v != p && v != blk) {
        vals.pb(calc(v, u, blk));
    }
    sort(rall(vals));
    F0R(i, sz(vals)) ckmax(dp[u], vals[i] + i + 1);
    return dp[u];
}

void solve() {
    cin >> N >> A >> B;
    F0R(i, N-1) {
        int u, v;
        cin >> u >> v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    dfs(A, -1);
    int lo = 0, hi = sz(pathAB) - 2;
    while(lo < hi) {
        int mid = lo + (hi - lo + 1)/2;
        int resA = calc(A, -1, pathAB[mid+1]);
        int resB = calc(B, -1, pathAB[mid]);
        if(resA <= resB) lo = mid;
        else hi = mid-1;
    }
    int ans = max(calc(A, -1, pathAB[lo+1]), calc(B, -1, pathAB[lo]));
    if(lo + 2 < sz(pathAB)) ckmin(ans, max(calc(B, -1, pathAB[lo+1]), calc(A, -1, pathAB[lo+2])));
    cout << ans << nl;
}

int main() {
    setIO();

    int t=1;
    //cin>>t;
    while(t-->0) {
        solve();
    }

    return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'void setIO(std::string)':
torrent.cpp:37:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen((NAME + ".inp").c_str(),"r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:38:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   38 |         freopen((NAME + ".out").c_str(),"w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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