Smallest substring of all characters - the solution passes all test cases, but time complexity should be reviewed.

smallestSubstringsOfAllCharacters_PeerPractice.cpp

#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>

using namespace std;

string getShortestUniqueSubstring( const vector<char>& arr, const string &str ) 
{
  // your code goes here
  unordered_set<char> set;
  
  for (int i = 0; i < arr.size(); i++) {
    set.emplace(arr[i]);
  }
  
  unordered_map<char, int> map;
  
  int head = 0;  
  int minLength = INT_MAX;
  int runner = 0;
  
  string result;
  
  while (runner < str.size() && head <= runner) {
    char currentChar = str[runner];
    
    if (set.count(currentChar) != 0) {
      map[currentChar]++;
    }
    
    if (map.size() == set.size()) {
      int distance = runner - head + 1; 
      
      if (distance < minLength) {
          minLength = distance;
          result = str.substr(head, distance);
      }
      
      head++;
      runner = head - 1;  // ? 
      
      map.clear();
    }
    
    runner++;  
  }  
  
  if (minLength == INT_MAX)
    return "";
  
  return result;
}

int main() {
 
  return 0;
}

/*
xxxyz -> xyz


xyyzyzyx
xyyz -> extra y "xyyz" -> minSubtring
xxxyyz -> extra 2 -> dictionary<'x',  -2>, xx -> xyyz -> "xyyz"
O(n) -> 

axyz -> "axyz" -> 'a' -> "xyz"

hard level -> 30 minutes 
^
[x, y, z]

time complexity 

*/