백준 C# 1157

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace baek2
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            string lower_input = input.ToUpper();
            char[] arr = lower_input.ToArray();
        
            Dictionary<char, int> pig = new Dictionary<char, int>();
  
            for (int i = 0; i < input.Length; i++)
            {
                if (pig.ContainsKey(arr[i]))
                {
                    pig[arr[i]] += 1;
                }
                else
                {
                    pig.Add(arr[i], 1);
                }
            }
            int max = 0;
            char answer = 'a';
            foreach (KeyValuePair<char, int> i in pig)
            {
                if (max < i.Value)
                {
                    //Console.WriteLine($"max < i {i} {max}");
                    max = i.Value;
                    answer = i.Key;
                }
                else if (max == i.Value)
                {
                    //Console.WriteLine($"max == i {i} {max}");
                    answer = '?';
                }
            }
            Console.WriteLine(answer);
        }
    }
}