Submission #559055

#	Time	Username	Problem	Language	Result	Execution time	Memory
559055		Mamedov	Stations (IOI20_stations)	C++17	100 / 100	782 ms	840 KiB

stations

#include "stations.h"
#include <bits/stdc++.h>

using namespace std;

/*
  Label v with tin[v] for even levels and tout[v] for odd levels.
  This gives us labels of even numbers between [0, 2*n-2].
  We can divide each label by 2, so we get all labels in [0, n-1]

  Note: We can always restore [tin[v], tout[v]] by v and its neighbors' labels.
*/

void dfs(int v, int par, int level, int &timer, vector<int> &tin, vector<int> &tout, vector<int> &labels, vector<vector<int>> &g) {
  tin[v] = timer++;
  for (int to : g[v]) {
    if (to != par) {
      dfs(to, v, level + 1, timer, tin, tout, labels, g);
    }
  }
  tout[v] = timer++;
  if (level % 2 == 0) {
    labels[v] = tin[v] / 2;
  } else {
    labels[v] = tout[v] / 2;
  }
}

vector<int> label(int n, int k, vector<int> u, vector<int> v) {
  vector<vector<int>>g(n);
  vector<int>tin(n), tout(n);
  vector<int>labels(n);
  int timer = 0;
  for (int i = 0; i < n - 1; ++i) {
    g[u[i]].emplace_back(v[i]);
    g[v[i]].emplace_back(u[i]);
  }
  dfs(0, 0, 0, timer, tin, tout, labels, g);
  return labels;
}

int find_next_station(int s, int t, vector<int> c) {
  if (c[0] > s) {  /// s is labeled with tin[]
    if (t < s) {
      return c.back();
    } else {
      auto itr = lower_bound(c.begin(), c.end(), t);
      if (itr == c.end()) --itr;
      return (*itr);
    }
  } else {  /// s is labeled with tout[]
    if (t > s) {
      return c[0];
    } else {
      auto itr = upper_bound(c.begin(), c.end(), t);
      if (itr != c.begin()) --itr;
      return (*itr);
    }
  }
}

• Subtask 1: 5 / 5
• Subtask 2: 8 / 8
• Subtask 3: 16 / 16
• Subtask 4: 10 / 10
• Subtask 5: 61 / 61