Problem p03037 (C++)

Buggy submission (status: Runtime Error):
#include "bits/stdc++.h"
#define rep(i, j) for (int i = 0; i < j; i++)
using namespace std;
using ll = long long;

const int INF = 1001001001;

/*struct mint {
    ll x; // typedef long long ll;
    mint(ll x = 0) :x((x% mod + mod) % mod) {}
    mint operator-() const { return mint(-x); }
    mint& operator+=(const mint a) {
        if ((x += a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator-=(const mint a) {
        if ((x += mod - a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this; }
    mint operator+(const mint a) const { return mint(*this) += a; }
    mint operator-(const mint a) const { return mint(*this) -= a; }
    mint operator*(const mint a) const { return mint(*this) *= a; }
    mint pow(ll t) const {
        if (!t) return 1;
        mint a = pow(t >> 1);
        a *= a;
        if (t & 1) a *= *this;
        return a;
    }

    // for prime mod
    mint inv() const { return pow(mod - 2); }
    mint& operator/=(const mint a) { return *this *= a.inv(); }
    mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream& operator>>(istream & is, const mint & a) { return is >> a.x; }
ostream& operator<<(ostream & os, const mint & a) { return os << a.x; }*/

int main() {
  int n, m;
  cin >> n >> m;
  vector<int> l(n / 2);
  vector<int> r(n / 2);
  int ans = 0;
  int min = 1;
  int max = INF;
  rep(i, m) cin >> l[i] >> r[i];

  for (int i = 0; i < m; i++) {
    if (min <= l[i])
      min = l[i];
    if (max >= r[i])
      max = r[i];
  }

  if (max < min) {
    cout << 0 << endl;
    return 0;
  }

  cout << max - min + 1 << endl;
  return 0;
}


Fixed submission:
#include "bits/stdc++.h"
#define rep(i, j) for (int i = 0; i < j; i++)
using namespace std;
using ll = long long;

const int INF = 1001001001;

/*struct mint {
    ll x; // typedef long long ll;
    mint(ll x = 0) :x((x% mod + mod) % mod) {}
    mint operator-() const { return mint(-x); }
    mint& operator+=(const mint a) {
        if ((x += a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator-=(const mint a) {
        if ((x += mod - a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this; }
    mint operator+(const mint a) const { return mint(*this) += a; }
    mint operator-(const mint a) const { return mint(*this) -= a; }
    mint operator*(const mint a) const { return mint(*this) *= a; }
    mint pow(ll t) const {
        if (!t) return 1;
        mint a = pow(t >> 1);
        a *= a;
        if (t & 1) a *= *this;
        return a;
    }

    // for prime mod
    mint inv() const { return pow(mod - 2); }
    mint& operator/=(const mint a) { return *this *= a.inv(); }
    mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream& operator>>(istream & is, const mint & a) { return is >> a.x; }
ostream& operator<<(ostream & os, const mint & a) { return os << a.x; }*/

int main() {
  int n, m;
  cin >> n >> m;
  vector<int> l(m);
  vector<int> r(m);
  int ans = 0;
  int min = 1;
  int max = INF;
  rep(i, m) cin >> l[i] >> r[i];

  for (int i = 0; i < m; i++) {
    if (min <= l[i])
      min = l[i];
    if (max >= r[i])
      max = r[i];
  }

  if (max < min) {
    cout << 0 << endl;
    return 0;
  }

  cout << max - min + 1 << endl;
  return 0;
}