find the second highest frequency of the character in the string

Question

I want to find the second highest frequency of the character in the string. For example: abccddd

O/p should be : c

I tried with dictionary. I am storing everything in dictionary. Moreover, I am also sorting it. Now I dont know how should I proceed.

string input = tb_input.Text;
Dictionary<string, int> di = new Dictionary<string, int>();

for (int i = 0; i < input.Length; i++)
{
    if (di.ContainsKey(input[i].ToString()))
    {
        int value = di[input[i].ToString()];               
        value++;

        di[input[i].ToString()] = value;
    }
    else
    {
        di.Add(input[i].ToString(), 0);
    }
}

var items = di.Values.ToList();

items.OrderByDescending(x => x).ToList();

Answer 1

You're only storing number of occurrences in items . You should store character as well:

var items = di.OrderByDescending(x => x.Value).ToList();

return items[1].Key;

Also, why do you start with 0 ? You should probably add 1 to dictionary, when it's not already there:

else
{
    di.Add(input[i].ToString(), 1);
}

Update

Just to let you know, it can be easily solved using LINQ:

return input.GroupBy(x => x).OrderByDescending(x => x.Count()).ElementAt(1).Key;