Hashset mock interview algorithm

HashSet_solution_discussion.cpp

/*
Given a set of strings, e.g. {“one”, “cat”, “two”, “four”}, 
and a target string, e.g. “fouroneone”, return true if the target string is 
composed of elements from the set. 	

“onecat” -> true
“fouron” -> false
“twone” -> false

one, cat, two, four

a target string fouroneone
target string is composed of elementes from the set
*/
bool isValidConcatination(string input, unordered_map<string> UMStr,
unordered_map<string, bool> Visited){
    
    if(input.size() == 0){
        return true;
    }
      
    
    if(Visited.count(input)){ // here I'm checking if I have alredy vistited that string...if yes I return from here...
        return Visited[input];
    }
        
    for(int len = 1; len < input.size(); len++)
     {
         string substr = input.substr(0, len);  // all possible substring
         
         // means valid string  or here we can use trie to check is alid string..
         if(UMStr.count(substr))
         {
             if(isValidConcatination(input.substr(len), UMstr))
                 ->put something true in the memo 
                 return true;
         }         
     }
  
  Visited[input] = false; // I'm in doubt...  
  return false;  
}