Submission #1112186

#	Time	Username	Problem	Language	Result	Execution time	Memory
1112186		vjudge1	Palembang Bridges (APIO15_bridge)	C++17	100 / 100	115 ms	13492 KiB

bridge

#include <iostream>
#include <vector>
#include <algorithm>
#include <array>
using namespace std;

int main() {
  int K, n;
  cin >> K >> n;

  vector<pair<long long, long long>> citizens;
  long long basicCost = 0;
  for (int i = 0;i < n; ++i) {
    long long x, y;
    char a, b;
    cin >> a >> x >> b >> y;
    if (a == b) {
      basicCost += abs(x-y);
    } else {
      basicCost += 1;
      if (x > y) citizens.push_back({y, x});
      else citizens.push_back({x, y});
    }
  }
  sort(citizens.begin(), citizens.end(), [](const pair<long long, long long>& a, const pair<long long, long long>& b) {
    return a.first + a.second < b.first + b.second;
  });
  vector<array<long long, 3>> points;
  points.push_back({0, -1, -1}); // add a fake point for easy boundary handling.
  for (int i = 0; i < citizens.size(); ++i) {
    points.push_back({citizens[i].first, 0, i});
    points.push_back({citizens[i].second, 1, i});
  }
  sort(points.begin(), points.end());
  /*
  cerr << "init, bcost:" << basicCost << " citizens:" << citizens.size() << endl;
  for (auto p : points) {
    cerr << "dist:" << p[0] << " pt:" << p[1] << "  idx:" << p[2] << endl;
  }
  */

  long long rightCost = 0;
  for (auto& ctz : citizens) {
    rightCost += ctz.first + ctz.second;
  }
  int rightIndex = 0;
  int rightBehind = 0, rightAhead = citizens.size();
  while (rightBehind < rightAhead) {
    ++rightIndex;
    rightCost += (rightBehind - rightAhead) * 2 * (points[rightIndex][0] - points[rightIndex - 1][0]);
    if (points[rightIndex][1] == 0) rightAhead -= 1;
    else if (points[rightIndex][1] == 1) rightBehind += 1;
  }
  if (K == 1) {
    cout << rightCost + basicCost << endl;
    return 0;
  }
  long long bestCost = rightCost;

  long long leftCost = 0;
  int leftIndex = 0, leftAhead = 0, leftBehind = 0;
  for (int mid = 0; mid + 1 < citizens.size(); ++mid) {
    // cerr << "----- " << "round " << mid << endl;
    // Reduce the effect of mid from right side.
    if (array<long long, 3>({citizens[mid].first, 0, mid}) > points[rightIndex]) {
      rightAhead -= 1;
      rightCost -= citizens[mid].first + citizens[mid].second - 2 * points[rightIndex][0];
    } else if (array<long long, 3>({citizens[mid].second, 1, mid}) <= points[rightIndex]) {
      rightBehind -= 1;
      rightCost -= - (citizens[mid].first + citizens[mid].second) + 2 * points[rightIndex][0];
    } else {
      rightCost -= citizens[mid].second - citizens[mid].first;
    }
    while (rightBehind < rightAhead) {
      rightIndex += 1;
      rightCost += (rightBehind - rightAhead) * 2 * (points[rightIndex][0] - points[rightIndex - 1][0]);
      if (points[rightIndex][2] > mid) {
        if (points[rightIndex][1] == 0) rightAhead -= 1;
        else rightBehind += 1;
      }
    }

    // Add the cost of newly added stuff.
    if (array<long long, 3>({citizens[mid].first, 0, mid}) > points[leftIndex]) {
      leftAhead += 1;
      leftCost += citizens[mid].first + citizens[mid].second - 2 * points[leftIndex][0];
    } else if (array<long long, 3>({citizens[mid].second, 1, mid}) <= points[leftIndex]) {
      leftBehind += 1;
      leftCost += - (citizens[mid].first + citizens[mid].second) + 2 * points[leftIndex][0];
    } else {
      leftCost += citizens[mid].second - citizens[mid].first;
    }
    while (leftBehind < leftAhead) {
      leftIndex += 1;
      leftCost += (leftBehind - leftAhead) * 2 * (points[leftIndex][0] - points[leftIndex - 1][0]);
      if (points[leftIndex][2] <= mid) {
        if (points[leftIndex][1] == 0) leftAhead -= 1;
        else leftBehind += 1;
      }
    }
/*
    cerr << "Round: " << mid << endl;
    cerr << rightCost<< ": " << rightIndex << " " << rightAhead << ":" << rightBehind << endl;
    cerr << leftCost << ": " << leftIndex << " " << leftAhead << ":" << leftBehind << endl;
    */
    if (leftCost + rightCost < bestCost) {
      bestCost = leftCost + rightCost;
    }
  }

  cout << bestCost + basicCost << endl;
  return 0;
}

Compilation message (stderr)

bridge.cpp: In function 'int main()':
bridge.cpp:30:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   30 |   for (int i = 0; i < citizens.size(); ++i) {
      |                   ~~^~~~~~~~~~~~~~~~~
bridge.cpp:62:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   62 |   for (int mid = 0; mid + 1 < citizens.size(); ++mid) {
      |                     ~~~~~~~~^~~~~~~~~~~~~~~~~

• Subtask 1: 8 / 8
• Subtask 2: 14 / 14
• Subtask 3: 9 / 9
• Subtask 4: 32 / 32
• Subtask 5: 37 / 37