Language: C++

#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using piii = pair<int, pii>;
using plll = pair<ll, pll>;
using pib = pair<int, bool>;
using pdi = pair<double, int>;
using pid = pair<int, double>;
using ld = long double;
using piiii = pair<pii, pii>;

#define endl "\n"
#define inf 0x3f3f3f3f3f
#define f first
#define s second

ll gcd(ll a, ll b){return b == 0 ? a : gcd(b, a % b);}
ll lcm(ll a, ll b){return a*b/gcd(a,b);}
ll fpow(ll  b, ll exp, ll mod){if(exp == 0) return 1;ll t = fpow(b,exp/2,mod);if(exp&1) return t*t%mod*b%mod;return t*t%mod;}
ll divmod(ll i, ll j, ll mod){i%=mod,j%=mod;return i*fpow(j,mod-2,mod)%mod;}

int n;
ll a, b, pre[100005], suf[100005];
vector<pii> arr;

bool cmp(pii &p1, pii &p2){
    if (p1.s==p2.s) return p1.f>p2.f;
    return p1.s>p2.s;
}


int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    ll ans = 0;
    for (int i=0; i<n; i++){
        cin >> a >> b;
        ans = max(ans, b-a+1);
        arr.push_back({a, b});
    }
    sort(arr.begin(), arr.end());
    ll l = 1;
    ll r = 1e9;
    for (int i=arr.size()-1; i>=0; i--){
        l = max(l, arr[i].f);
        r = min(r, arr[i].s);
        if (l>r) break;
        suf[i] = r-l+1;
    }
    l = 1;
    r = 1e9;
    for (int i=0; i<arr.size(); i++){
        l = max(l, arr[i].f);
        r = min(r, arr[i].s);
        if (l>r) break;
        ans = max(ans, r-l+1+suf[i+1]);
    }
    sort(arr.begin(), arr.end(), cmp);
    l = 1;
    r = 1e9;
    for (int i=arr.size()-1; i>=0; i--){
        l = max(l, arr[i].f);
        r = min(r, arr[i].s);
        if (l>r) break;
        pre[i] = r-l+1;
    }
    l = 1;
    r = 1e9;
    for (int i=0; i<arr.size(); i++){
        l = max(l, arr[i].f);
        r = min(r, arr[i].s);
        if (l>r) break;
        ans = max(ans, r-l+1+pre[i+1]);
    }
    assert(ans>0&&ans<2e9+1);
    cout << ans << endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:53:16: error: no matching function for call to 'max(ll&, int&)'
   53 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:53:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   53 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:53:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   53 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
a.cc:54:16: error: no matching function for call to 'min(ll&, int&)'
   54 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:54:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   54 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5696:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::min(initializer_list<_Tp>, _Compare)'
 5696 |     min(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5696:5: note:   template argument deduction/substitution failed:
a.cc:54:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   54 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
a.cc:61:16: error: no matching function for call to 'max(ll&, int&)'
   61 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:61:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   61 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:61:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   61 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
a.cc:62:16: error: no matching function for call to 'min(ll&, int&)'
   62 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:62:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   62 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5696:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::min(initializer_list<_Tp>, _Compare)'
 5696 |     min(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5696:5: note:   template argument deduction/substitution failed:
a.cc:62:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   62 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
a.cc:70:16: error: no matching function for call to 'max(ll&, int&)'
   70 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:70:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   70 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:70:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   70 |         l = max(l, arr[i].f);
      |             ~~~^~~~~~~~~~~~~
a.cc:71:16: error: no matching function for call to 'min(ll&, int&)'
   71 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:71:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   71 |         r = min(r, arr[i].s);
      |             ~~~^~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/