Submission #676717

#	Time	Username	Problem	Language	Result	Execution time	Memory
676717		d4xn	Race (IOI11_race)	C++17	100 / 100	1034 ms	46040 KiB

race

#pragma GCC optimize ("Ofast")
#include "race.h"
#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
 
const int N = 2e5+1;
const ll inf = LLONG_MAX;
 
int n, k, sz[N];
ll ans;
vector<pair<int, ll>> adj[N];
bitset<N> r;
 
void dfs(int u, int par) {
  sz[u] = 1;
  for (auto &[v, w] : adj[u]) {
    if (v == par || r[v]) continue;
    dfs(v, u);
    sz[u] += sz[v];
  }
}
 
int find_centroid(int u, int par, int rt) {
  for (auto &[v, w] : adj[u]) {
    if (v != par && !r[v] && sz[v] > sz[rt]/2) {
      return find_centroid(v, u, rt);
    }
  }
  return u;
}
 
void dfs2(int u, int par, ll d, ll dw, map<ll, ll> &dis) {
  if (dw > k || d >= ans) return;
  auto it = dis.find(dw);
  if (it == dis.end()) dis[dw] = d;
  else it->second = min(it->second, d);
 
  for (auto &[v, w] : adj[u]) {
    if (v == par || r[v]) continue;
    dfs2(v, u, d+1, dw+w, dis);
  }
}
 
void solve_centroid(int u) {
  map<ll, ll> mnD;
  mnD[0] = 0;
  for (auto &[v, w] : adj[u]) {
    if (r[v]) continue;
    map<ll, ll> mnD2;
    dfs2(v, u, 1, w, mnD2);
    if (mnD2.size() > mnD.size()) swap(mnD, mnD2);
 
    for (auto &[dw, d] : mnD2) {
        auto it = mnD.find(k-dw);
        if (it == mnD.end()) continue;
        ans = min(ans, d+it->second);
    }
 
    for (auto &[dw, d] : mnD2) {
        auto it = mnD.find(dw);
        if (it == mnD.end()) mnD[dw] = d;
        else it->second = min(it->second, d);
    }
  }
}
 
void dec(int u) {
  dfs(u, u);
  int ct = find_centroid(u, u, u);
  r[ct] = 1;
  solve_centroid(ct);
  for (auto &[v, w] : adj[ct]) {
    if (r[v]) continue;
    dec(v);
  }
}

int best_path(int N, int K, int H[][2], int L[]) {
  ans = inf;
  n = N;
  k = K;
  for (int i = 0; i < n-1; i++) {
    adj[H[i][0]].push_back(make_pair(H[i][1], L[i]));
    adj[H[i][1]].push_back(make_pair(H[i][0], L[i]));
  }
  dec(0);
  return (ans == inf ? -1 : ans);
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 57 / 57