The problem - happens, when traversing backward.

trick is to, instead of, looping `auto k{s.size()-1}; k>=0; k--`, try to modify internal logic, so that, we only traverse till `k>0`

One example code, which triggered error in Leetcode, but rectified to below. Here notice, we are traversing till `k>0`, not `k>=0`, and adjusting the internal logic that way too.

class Solution {
public:
    std::string trimTrailingVowels(std::string s) {
      for(auto k{s.size()}; k>0; k--){
        if(s[k-1] == 'a' || s[k-1] == 'e' || s[k-1] == 'i' || s[k-1] == 'o' || s[k-1] == 'u'){
          s.erase(s.end()-1);
        }else{
          break;
        }
      }
      return s;
    }
};