Problem p02575 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <iostream>
#include <map>
#include <set>
#include <vector>
using namespace std;

template <class K, class V>
ostream &operator<<(ostream &out, const map<K, V> m) {
  out << "Dict(size=" << m.size() << ", ";
  out << "{ ";
  for (auto &[k, v] : m) {
    out << k << ": " << v << ", ";
  }
  out << "})";
  return out;
}

template <class T> ostream &operator<<(ostream &out, const multiset<T> s) {
  out << "Set(size=" << s.size() << ", ";
  out << "{ ";
  for (auto it = s.begin(); it != s.end(); ++it) {
    out << *it << " ";
  }
  out << "})";
  return out;
}

void solve() {
  int H, W;
  cin >> H >> W;

  multiset<int> steps;
  map<int, int> end2start;
  for (int c = 0; c < W; c++) {
    end2start[c] = c;
    steps.insert(0);
  }

  for (int r = 1; r <= H; r++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;

    // Erase pairs (e, s) that a <= e <= b + 1
    auto lb = end2start.lower_bound(a);
    auto ub = end2start.upper_bound(b + 1);
    auto max_start = -1;
    for (auto it = lb; it != ub; ++it) {
      int end = it->first;
      int start = it->second;
      steps.erase(steps.find(end - start));
      max_start = max(max_start, start);
    }
    end2start.erase(lb, ub);

    // Update pair (b + 1, s)
    if (b != W - 1 and max_start != -1) {
      end2start[b + 1] = max_start;
      steps.insert(b + 1 - end2start[b + 1]);
    }

    if (steps.size() > 0) {
      cout << *steps.begin() + r << endl;
    } else {
      cout << "-1" << endl;
    }
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  solve();
  return 0;
}

Error: 0

Fixed submission:

#include <algorithm>
#include <iostream>
#include <map>
#include <set>
#include <vector>
using namespace std;

template <class K, class V>
ostream &operator<<(ostream &out, const map<K, V> m) {
  out << "Dict(size=" << m.size() << ", ";
  out << "{ ";
  for (auto &[k, v] : m) {
    out << k << ": " << v << ", ";
  }
  out << "})";
  return out;
}

template <class T> ostream &operator<<(ostream &out, const multiset<T> s) {
  out << "Set(size=" << s.size() << ", ";
  out << "{ ";
  for (auto it = s.begin(); it != s.end(); ++it) {
    out << *it << " ";
  }
  out << "})";
  return out;
}

void solve() {
  int H, W;
  cin >> H >> W;

  multiset<int> steps;
  map<int, int> end2start;
  for (int c = 0; c < W; c++) {
    end2start[c] = c;
    steps.insert(0);
  }

  for (int r = 1; r <= H; r++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;

    auto lb = end2start.lower_bound(a);
    auto ub = end2start.upper_bound(b);
    auto max_start = -1;
    for (auto it = lb; it != ub; ++it) {
      int end = it->first;
      int start = it->second;
      steps.erase(steps.find(end - start));
      max_start = max(max_start, start);
    }
    end2start.erase(lb, ub);

    if (b != W - 1 and max_start != -1) {
      auto it = steps.find(b + 1 - end2start[b + 1]);
      if (it != steps.end()) {
        steps.erase(it);
      }
      end2start[b + 1] = max(end2start[b + 1], max_start);
      steps.insert(b + 1 - end2start[b + 1]);
    }

    if (steps.size() > 0) {
      cout << *steps.begin() + r << endl;
    } else {
      cout << "-1" << endl;
    }
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  solve();
  return 0;
}