《結城浩のスペーストーキー問題》

Main.java

import java.io.BufferedReader;
import java.io.InputStreamReader;

class Main {
  private static String encodeStringFromChar2(char c, int n) {
    StringBuffer buf = new StringBuffer();
    for(int i = 0; n > 0 ; i++) {
      buf.append(c); 
      buf.append((char)('a' + ((n > 26)? 25 : n - 1)));
      n -= 26;
    }
    return buf.toString();
  }
  private static String myEncode(char[] str, int n) {
    StringBuffer buf = new StringBuffer();
    int i = 0;
    while(i < n) {
       char c = str[i];
       int  m = i;
       while(i < n && c == str[i]) i++; 
       buf.append(encodeStringFromChar2(c, i - m));
    }
    return buf.toString();
  }
  private static String myDecode(char[] str, int n) {
    StringBuffer buf = new StringBuffer();
    for(int i = 0; i < n; i++) {
       char c = str[i++];
       int  m = str[i] - 'a' + 1;
       buf.append(decodeStringFromChar(c, m));
    }
    return buf.toString();
  }
  private static String decodeStringFromChar(char c, int n) {
    char[] value = new char[n];
    for(int i = 0; i < n; i++) value[i] = c;  
    return new String(value);
  }
  public static void main(String[] args) throws Exception {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String line = null;
    while((line = br.readLine()) != null) {
      int n = line.length();
      char[] a = line.toCharArray();
      if(n % 2 != 0) System.out.println("X:" + line);
      else {
       String decoded = myDecode(a, n);
       int m = decoded.length();
       boolean isValid = m <= 1024 && 
                         line.equals(myEncode(decoded.toCharArray(), m));
       if(isValid)
         System.out.println(decoded + ":" + line);
       else
         System.out.println("X:" + line);
      }
    } 
  }
}