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PO3n+1 challenge at UVa
 

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    <p>I'm having trouble running the "3n+1 Problem" from the "Programming Challenges" <a href="http://programming-challenges.com/pg.php?page=downloadproblem&amp;probid=110101&amp;format=html" rel="nofollow">book</a>.</p> <p>I've tried every solution in Java I could find on google (even the ones on Stack Overflow), and not a single one works, they all report a "Wrong answer". I also found a working C++ solution, translated it to Java, and same thing: "Wrong answer".</p> <p>I'm using the template from Programming Challenges for Java <a href="http://programming-challenges.com/pg.php?page=javainfo" rel="nofollow">submissions</a>, and I could swear my algorithm is right, the only possible problem I can think of is in the code for reading the input or writing the output, but I can't figure it out. Here's my code, any help would be greatly appreciated:</p> <pre><code>class myStuff implements Runnable { @Override public void run() { String line = Main.ReadLn(128); while (line != null) { process(line); line = Main.ReadLn(128); } } private void process(String line) { String[] data = line.split("\\s+"); if (data.length == 2) { int low = Integer.parseInt(data[0]); int high = Integer.parseInt(data[1]); int max = low &lt; high ? findMax(low, high) : findMax(high, low); System.out.println(low + " " + high + " " + max); } } private int findMax(int low, int high) { int max = Integer.MIN_VALUE; for (int i = low; i &lt;= high; i++) { int length = cycleLength(i); if (length &gt; max) max = length; } return max; } private int cycleLength(int i) { long n = i; int length = 1; while (n &gt; 1) { n = ((n &amp; 1) == 0) ? n &gt;&gt; 1 : 3*n + 1; length++; } return length; } } // java program model from www.programming-challenges.com class Main implements Runnable { static String ReadLn(int maxLength) { // utility function to read from // stdin, Provided by Programming-challenges, edit for style only byte line[] = new byte[maxLength]; int length = 0; int input = -1; try { while (length &lt; maxLength) { // Read untill maxlength input = System.in.read(); if ((input &lt; 0) || (input == '\n')) break; // or untill end of line ninput line[length++] += input; } if ((input &lt; 0) &amp;&amp; (length == 0)) return null; // eof return new String(line, 0, length); } catch (java.io.IOException e) { return null; } } public static void main(String args[]) { // entry point from OS Main myWork = new Main(); // Construct the bootloader myWork.run(); // execute } @Override public void run() { new myStuff().run(); } } </code></pre>
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    1. USCharles
    1. USÓscar López
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    1. COCan you run your program yourself against sample data? Does it produce correct answers?
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    2. COYes, it does run fine - with correctly formatted input. That was the problem, I should not have assumed that the input was properly formatted, and program in a defensive style
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      1. USÓscar López
 

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