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  1. import java.security.MessageDigest;
  2. import java.security.NoSuchAlgorithmException;
  3. import java.util.Arrays;
  4.  
  5. class Ideone {
  6.  
  7.     /** 解析したいMD5ハッシュ */
  8.     private static final byte[] TARGET = decodeHex("ab56b4d92b40713acc5af89985d4b786");
  9.  
  10.     /** ループ回数 */
  11.     private static final long CHALLENGE_MAX = Long.parseLong("zzzzzz", Character.MAX_RADIX);
  12.  
  13.     private static MessageDigest digest;
  14.  
  15.     public static void main(String[] args) {
  16.  
  17.         String challenge;
  18.         for (long i = 0; i < CHALLENGE_MAX; i++) {
  19.             challenge = Long.toString(i, Character.MAX_RADIX);
  20.             byte[] digest = getDigest().digest(challenge.getBytes());
  21.  
  22.             if (Arrays.equals(TARGET, digest)) {
  23.                 System.out.println("やりました");
  24.                 System.out.println("答えは " + challenge);
  25.                 break;
  26.             }
  27.             if (i % 1000000 == 0) {
  28.                 System.out.println(i + "回目の試行..." + challenge);
  29.             }
  30.         }
  31.     }
  32.  
  33.     /**
  34.      * メッセージダイジェストのインスタンスを取得
  35.      * 
  36.      * @param algorithm アルゴリズム
  37.      * @return
  38.      */
  39.     private static MessageDigest getDigest() {
  40.         if (digest != null) {
  41.             return digest;
  42.         }
  43.         try {
  44.             return digest = MessageDigest.getInstance("MD5");
  45.         } catch (NoSuchAlgorithmException e) {
  46.             throw new RuntimeException(e.getMessage());
  47.         }
  48.     }
  49.  
  50.     /**
  51.      * 16進数文字列をバイト配列にする
  52.      * 
  53.      * @param str
  54.      * @return
  55.      */
  56.     public static byte[] decodeHex(String str) {
  57.         final char[] data = str.toCharArray();
  58.         final int len = data.length;
  59.         final byte[] out = new byte[len >> 1];
  60.         // two characters form the hex value.
  61.         for (int i = 0, j = 0; j < len; i++) {
  62.             int f = Character.digit(data[j], 16) << 4;
  63.             j++;
  64.             f = f | Character.digit(data[j], 16);
  65.             j++;
  66.             out[i] = (byte) (f & 0xFF);
  67.         }
  68.         return out;
  69.     }
  70. }
  71.  
Time limit exceeded #stdin #stdout 5s 380672KB
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stdin
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Standard input is empty
stdout
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0回目の試行...0
1000000回目の試行...lfls
2000000回目の試行...16v7k
3000000回目の試行...1satc
4000000回目の試行...2dqf4
https://ideone.com/0J8J9F
language:
Java (HotSpot 12)
created:
10 years ago
visibility:
public

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