Runtime error for C++ code when using a user defined explicit function to sort a vector of pairs

Question

I am receiving a runtime error in this code and I am not able to understand the reason.Can anyone help me out and could tell me the reason and the type of runtime error i am getting? I have been solving this question from codeforces,so here i am attaching the link of that submission so that you could see the actual test case in which i am getting this error.Here's the link https://codeforces.com/contest/1294/submission/113416390 .And here's the code

#include <bits/stdc++.h> // Include every standard library 
//#include <boost/math/common_factor.hpp>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
bool cmp(pair<int,int>&p1,pair<int,int>&p2)
{
    return (p1.first<=p2.first);
}
bool cmpp(pair<int,int>&p1,pair<int,int>&p2)
{
    return (p1.second<p2.second);
}
int main()
{
    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
  int t;
    cin >> t;
    
    while (t--) 
    {
      int n;
      cin>>n;
      string s;
      int x{},y{};
      int arr[n],brr[n];
      vector<pair<int,int>>vec;
      for(int i=0;i<n;i++)
      {
         
          cin>>arr[i]>>brr[i];
          vec.push_back({arr[i],brr[i]});
      }
        
      sort(vec.begin(),vec.end(),cmp);
      
    if(!is_sorted(vec.begin(),vec.end(),cmpp))
    cout<<"NO"<<endl;
    else
    {
        cout<<"YES"<<endl;
        sort(arr,arr+n);
        sort(brr,brr+n);
        for(int i=0;i<n;i++)
        {
          if(arr[i]!=x)
          s.append((arr[i]-x),'R');
          if(brr[i]!=y)
          s.append((brr[i]-y),'U');
          x=arr[i];
          y=brr[i];
        }
        cout<<s<<endl;
    }
    
    }
return 0;
}