Dictionary to return a character list with their indices-CodePudding

I've been tasked with taking a string and returning a dictionary that has a map of characters to a list of their indices in a given string. The output should show which characters occur where in the given string. I am currently stumped on where to go from the code I will post below.

public Dictionary<string, List<int>> returnDictionary(string s)
        {
             Dictionary<string, List<int>> newDictionary = new Dictionary<string, List<int>>();
            char[] strArray = s.ToCharArray();
            List<char> strList = strArray.ToList();
            List<int> charIndex;
            for (int i = 0; i < strList.Count(); i  )
            {
                if (!newDictionary.TryGetValue(strList[i].ToString(), out charIndex))
                {
                    newDictionary.Add(strList[i].ToString(), charIndex);
                }
            }
            return newDictionary;
        }

I have tests being ran in another file, when the test is ran, it should pass. Test related below:

        public void TestConcordanceForGoodString()
        {
            var input = "engineering";
            var eIndices = new int[3] { 0, 5, 6 };
            var nIndices = new int[3] { 1, 4, 9 };
            var gIndices = new int[2] { 2, 10 };
            var iIndices = new int[2] { 3, 8 };
            var rIndices = new int[1] { 7 };

            var actual = csharpLogic.ConcordanceForString(input);
            Assert.Equal(5, actual.Count);  //Ensure 5 total keys
            Assert.Equal(eIndices, actual["e"]); //Ensure the correct indices in the correct order
            Assert.Equal(nIndices, actual["n"]);
            Assert.Equal(gIndices, actual["g"]);
            Assert.Equal(iIndices, actual["i"]);
            Assert.Single(actual["r"]);

CodePudding user response：

This code passes the test:

public class CharacterIndexDictionary
{
    public static Dictionary<string, List<int>> ConcordanceForString(string input)
    {
        var result = new Dictionary<string, List<int>>();

        for (var index = 0; index < input.Length; index  )
        {
            // Get the character positioned at the current index.
            // We could just use input[index] everywhere, but
            // this is a little easier to read.
            string currentCharacter = input[index].ToString();

            // If the dictionary doesn't already have an entry
            // for the current character, add one.
            if (!result.ContainsKey(currentCharacter))
            {
                result.Add(currentCharacter, new List<int>());
            }

            // Add the current index to the list for
            // the current character.
            result[currentCharacter].Add(index);
        }

        return result;
    }
}

If I wanted to index characters I'd use a Dictionary<char, List<int>> instead of using a string as the key, but this uses string because the test requires it.

CodePudding user response：

This code block is like your code and in a way that you can understand

public Dictionary<string, List<int>> ConcordanceForString(string s)
    {
        Dictionary<string, List<int>> newDictionary = new Dictionary<string, List<int>>();

        List<char> charList = new List<char>();

        foreach (var item in s)
        {
            if (!charList.Any(x => x == item))
            {
                charList.Add(item);

                List<int> itemInds = new List<int>();
                
                for (int i = 0; i< s.Length; i  )
                {
                    if (s[i] == item)
                    {
                        itemInds.Add(i);
                    }
                }

                newDictionary.Add(item.ToString(), itemInds);
            }
        }

      
        return newDictionary;
    }