Submission #102845

#	Time	Username	Problem	Language	Result	Execution time	Memory
102845		wxh010910	Highway Tolls (IOI18_highway)	C++17	100 / 100	347 ms	11068 KiB

highway

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

using namespace std;

void find_pair(int n, vector<int> u, vector<int> v, int a, int b) {
  vector<vector<pair<int, int>>> adj(n);
  int m = u.size();
  vector<int> w(m);
  for (int i = 0; i < m; ++i) {
    adj[u[i]].emplace_back(v[i], i);
    adj[v[i]].emplace_back(u[i], i);
  }
  long long value = ask(w);
  int l = 0, r = m - 2, e = m - 1;
  while (l <= r) {
    int mid = l + r >> 1;
    for (int i = 0; i < m; ++i) {
      w[i] = i <= mid;
    }
    if (ask(w) != value) {
      e = mid;
      r = mid - 1;
    } else {
      l = mid + 1;
    }
  }
  vector<int> tree, left, right, visit(n);
  queue<int> q;
  q.push(u[e]);
  visit[u[e]] = 1;
  left.push_back(u[e]);
  q.push(v[e]);
  visit[v[e]] = 2;
  right.push_back(v[e]);
  tree.push_back(e);
  while (!q.empty()) {
    int x = q.front();
    q.pop();
    for (auto p : adj[x]) {
      int y = p.first, w = p.second;
      if (!visit[y]) {
        tree.push_back(w);
        q.push(y);
        if (visit[x] == 1) {
          visit[y] = 1;
          left.push_back(y);
        } else {
          visit[y] = 2;
          right.push_back(y);
        }
      }
    }
  }

  auto solve = [&](vector<int> nodes) {
    int l = 0, r = nodes.size() - 2, p = nodes.size() - 1;
    while (l <= r) {
      int mid = l + r >> 1;
      vector<bool> ban(n, false);
      for (int i = mid + 1; i < nodes.size(); ++i) {
        ban[nodes[i]] = true;
      }
      for (int i = 0; i < m; ++i) {
        w[i] = 1;
      }
      for (auto e : tree) {
        if (!ban[u[e]] && !ban[v[e]]) {
          w[e] = 0;
        }
      }
      if (ask(w) == value) {
        p = mid;
        r = mid - 1;
      } else {
        l = mid + 1;
      }
    }
    return nodes[p];
  };

  answer(solve(left), solve(right));
}

Compilation message (stderr)

highway.cpp: In function 'void find_pair(int, std::vector<int>, std::vector<int>, int, int)':
highway.cpp:17:17: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
     int mid = l + r >> 1;
               ~~^~~
highway.cpp: In lambda function:
highway.cpp:59:19: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
       int mid = l + r >> 1;
                 ~~^~~
highway.cpp:61:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       for (int i = mid + 1; i < nodes.size(); ++i) {
                             ~~^~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 6 / 6
• Subtask 4: 33 / 33
• Subtask 5: 18 / 18
• Subtask 6: 31 / 31