gistfile1.cs

using System;
using System.Collections.Generic;
using System.Text;
class MyClass {
    public void compute_palindromes(string[] words) {
        // Write your code here
        // To print results to the standard output you can use Console.WriteLine()
        // Example: Console.WriteLine("Hello world!");
        foreach(string word in words) {
            Dictionary<char, int> dict = createWordDict(word);
            if(canMakePaly(dict, word)) {
                Console.WriteLine(makePaly(dict));
            }
            else {
                Console.WriteLine(-1);
            }
            
        }
    }
    // this method can probably be optimized by calculating middle position of string builder
    private string makePaly(Dictionary<char, int> dict) {
        StringBuilder builder = new StringBuilder();
        // find middle character if one exists
        // and add it
        foreach(KeyValuePair<char, int> kv in dict) {
             int count1 = kv.Value;
            if(kv.Value %2 == 1) {
                while(count1 > 0) {
                    builder.Append(kv.Key);
                    count1--;
                }
                dict[kv.Key] = 0;
                break;
            }
        }
        
        foreach(KeyValuePair<char, int> kv in dict) {
            int count = kv.Value;
            //when alt = false add to beginning, when true add to end
            bool alternate = false;
           while(count > 0) {
               if(alternate) {
                   builder.Insert(0, kv.Key);
               }
               else {
                   builder.Append(kv.Key);
               }
               alternate = !alternate;
               count--;
           }
        }
        
        return builder.ToString();
    }
    
    private bool canMakePaly(Dictionary<char, int> dict, string word) {
       
        //if even char count
        //if any odd numbers is false
        bool ret = true;
        int threshold = word.Length % 2;
        int count = 0;
        foreach(KeyValuePair<char, int> k in dict) {
            if(k.Value %2 == 1) {
                count++;
                if(count > threshold) {
                      ret = false;
                      break;
                    }
                }
            }

        return ret;
    }
    
    public Dictionary<char, int> createWordDict(string word){ 
     Dictionary<char, int> dict = new Dictionary<char,int>();
        foreach(char c in word)    {
            if(!dict.ContainsKey(c)) {
                dict.Add(c, 0);
            }
            dict[c] = dict[c]+1;
        }
        return dict;
    }
}