public class Solution {
    public IList<int> FindSubstring(string s, string[] words) {
        var len = words[0].Length;
        var allLen = len*words.Length;
        var dict = new Dictionary<string, int>();
        foreach(var word in words)
        {
            dict.TryAdd(word, 0);
            dict[word]++;
        }
        var answer = new List<int>();
        var dictClone = new Dictionary<string, int>(dict);
        for(var i = 0; i < s.Length-allLen+1; i++)
        {
            var valid = 0;
            foreach (var kvp in dictClone)
                dictClone[kvp.Key] = dict[kvp.Key];
            for(var j=i; j < i+allLen; j+=len)
            {
                var word = s[j..(j+len)];
                if(dictClone.TryGetValue(word, out var count) && count > 0)
                {
                    dictClone[word]--;
                    valid++;
                }
                else
                {
                    break;
                }
            }
            if(valid == words.Length)
                answer.Add(i);
        }
        return answer;
    }
}