minimum substring - version 1, pass 2 test cases, fail 5 test cases.

minimumSubstring_P1.cs

using System;
using System.Linq; 

class Solution
{
    public static string GetShortestUniqueSubstring(char[] arr, string str)
    {
      if(arr == null || arr.Length == 0 || str.Length == 0) // false
            {
                return string.Empty; 
            }

            var length = arr.Length;// 3
            var searchLength = str.Length; // 8
            
            var minimumSubstring = "";
            var minimumLength = searchLength + 1;// 9 
            var uniqueCharsMet = 0; 

            int left = 0;

            var dictionary = arr.ToDictionary(c=>c, c=>1); // dictionary['x'] = 1, same as 'y', 'z'

            for (int index = 0; index < searchLength; index++) // 0, 1, 2, 3, 4
            {
                var visit = arr[index]; // 'x', 'y', 'y', 'z', 'y'
                var isInSet = dictionary.ContainsKey(visit); // true, true, true, true, true

                if(!isInSet)
                {
                    continue; 
                }

                var isNeeded = dictionary[visit] > 0; // true, true, false, true, false
                if(isNeeded)
                {
                    uniqueCharsMet++; // 1, 2, 3
                }

                dictionary[visit]--; // d['x'] = 0; d['y'] = 0; d['y'] = -1, d['z'] = 0, d['y'] = -2

                while(uniqueCharsMet == length) // 1 != 3, false; 2 != 3, false; 2!= 3, false; true, false
                {
                    // check to see if the left point can move forward
                    if(!dictionary.ContainsKey(arr[left]) || dictionary[arr[left]] <= 0) // "xyyz"
                    {
                        var current = arr[left]; // 'x'
                        var count = dictionary[current]; // 0
                        
                        if (count <= 0) // true
                        {
                            if (count == 0) 
                            {
                                uniqueCharsMet--; // 2
                            }

                            dictionary[current]++; // dictionary['x'] = 1
                        }

                        // maintain substring length
                        var startPosition = left; // 0 
                        var currentLength = index - startPosition + 1; // 4
                        var currentSubstring = str.Substring(startPosition, currentLength); //"xyyz"
                        if(currentLength < minimumLength) // 4 < 9
                        {
                            minimumLength = currentLength; // 4
                            minimumSubstring = currentSubstring; // "xyyz"
                        }

                        left++; // 1
                    }
                }
            }

            return minimumLength == (searchLength + 1) ? string.Empty : minimumSubstring; 
    }

    static void Main(string[] args)
    {

    }
}