Leetcode 76 - find smallest substring containing all characters in an array with distinct character. Need to work on the left point while loop.

Leetcode76_smallestSubstring.cs

using System;

class Solution
{
  // []'x','y','z'] - substring containing all characters
// find smallest -> minimum length 
//linear scan string -> O(n), visit char once 
// left point -> current point -> 
// index = 0 
// x -> hashmap -> Dictinary<char, int> 'x', 1 , 'y' 1, 'z' 1 
// x -> 'x' 1 - 1 -> 0 , no need 
// left 0 -> 
// y -> 'y' 1 -1 -> 0 -> variable to help to check if > 0 
// y -> 'y' 0 - 1 -> -1 
// z -> 'z' 1 - 1 -> 0  find word -> left 0, index = 3, "xyyz", length = 4, minimum
// left point -> x -> +1, need one x , value 1 > 0 
// go back step 18 or 19 
    public static string GetShortestUniqueSubstring(char[] arr, string str)
    {
      // your code goes here
      if(arr == null || arr.Length == 0)
      {
        return "";
      }
      
      // assume that arr is not empty
      if(str == null || str.Length == 0)
      {
        return "";
      }
      
      // put arr to the dictionary
      
      var map = new Dictionary<char, int>(); 
      foreach(var item in arr)
      {
        map.Add(item, 1); 
      }
      
      var needChars = arr.Length; // 'xyz' - 3, var match = needChars == 0 
      // iterate the string and find match, and also keep track of minimum 
      var left = 0; 
      var length = str.Length; 
      
      var smallestLength = length + 1;  // length + 1
      var smallestSubstring = ""; 
      //for(int index = 0; index < length; index++ )
      while()  
      {
        var visit = str[index]; 
        
        // x - 1 
        var needOne = map[visit] > 0; 
        map[visit] --; 
        if(needOne)
        {
          needChars --; // take x off 
        }
        
        var findMatch = needChars == 0; 
        if(findMatch)
        {
          var curentLength = index - left + 1; 
          var findSmallerOne = currentLength < smallestLength; 
          if(findSmallerOne)
          {
            smallestLength = curentLength; 
            smallestSubstring = str.Substring(left, index - left + 1); 
          }
          
          // move left point forward 
          var removeChar = str[left]; 
          
          // update the variable needChars xx -1
          var needIncrement = map[removeChar] == 0; 
          if(needIncrement)  // do a loop  - xxxxyz -> 6 -> xyz, do a loop to remove all 3 x -> xyz
          {
            needChars ++; 
          }
          
          map[removeChar] ++; // line 16
          left ++; 
          // 
        }
      }
      
      // edge case
      if(smallestLength == length + 1)
      {
        return "";
      }
      else
      {
        return smallestSubstring; 
      }
  
      
    }

    static void Main(string[] args)
    {

    }
}