smaller substring study code

smallestSubstring_studyCode.cs

using System;
using System.Collections.Generic;

class Solution
{
    public static string GetShortestUniqueSubstring(char[] arr, string str)
    {
      if (arr == null || str == null || arr.Length > str.Length) return "";
      
      int uCount = arr.Length;
      int n = str.Length;
      
      // Count of elements which are present in arr
      var count = new Dictionary<char, int>();
      
      int i, j;
      int min = Int32.MaxValue; // window length
      int start = -1; // answer start position
      
      for(i = 0; i < uCount; i++){
        count[arr[i]] = 0;
      }
      
      int found = 0; j = 0;
      for(i = 0; i <= n- uCount; i++)
      {     
        // at the end of this loop j should be pointing just at the end of thw windows
        
       
        while (found != uCount && j < n){
          if (count.ContainsKey(str[j])){
            if (count[str[j]] == 0){
              found++;
            }
            count[str[j]]++;
          }
          j++;
        }
        
        if (found == uCount && (j-i) < min){ // Found a new smaller window
          min = j-i;
          start = i;
        }
        
        // If the str[i] 
        if (count.ContainsKey(str[i])){
            if (count[str[i]] == 1){
              found--;
            }
            count[str[i]]--;
        }
      }
      
      if (start == -1) return "";
      
      return str.Substring(start, min);          
      
      
      
      
      /*
      xyyzyzyx
      i=0  left end of the window
      j =  right end of the window
      
      var count = int [256]
      [i,j] = find all the character of arr
      
      start with i = 0
      find j till all the characters in arr is covered
      window  - compare it with old window, if it smaller then save it.
      i = 1;
      decerment the value count[a[0]]--; it doesn't affect the all covering of element in arr
      remaining element is less than size of arr
      */
    }

    static void Main(string[] args)
    {
    }
}