Anagram - using Dictionary, keyValuePair class

Anagram4.cs

using System;
using System.Collections.Generic;
using System.IO;
class Solution {
    static void Main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
        int T = Int32.Parse(Console.ReadLine());
        for (int i = 0; i < T; i++) {
            string input = Console.ReadLine();
            Console.WriteLine(solve(input));
        }
    }
    
    private static int solve(string s) {
        if (s.Length % 2 != 0)
            return -1;
        
        int length = s.Length / 2;
        string a = s.Substring(0, length);
        string b = s.Substring(length, length);
        
        Dictionary<char,int> aChars = new Dictionary<char,int>();
        Dictionary<char,int> bChars = new Dictionary<char,int>();
        
        int different = 0;
        
        for (int i = 0; i < length; i++) {
            if (a[i] != b[length-1-i]) {
                if (!aChars.ContainsKey(a[i]))
                    aChars.Add(a[i], 1);
                else
                    aChars[a[i]]++;
                
                if (!bChars.ContainsKey(b[length-1-i]))
                    bChars.Add(b[length-1-i], 1);
                else
                    bChars[b[length-1-i]]++;
                
                different++;
            }
        }
        
        foreach (KeyValuePair<char,int> kvp in bChars) {            
            if (aChars.ContainsKey(kvp.Key)) {
                different -= Math.Min(aChars[kvp.Key], kvp.Value);
            }
        }
        
        return different;
    }
}