Array sometimes doesn't work as expected

Question

I've got a game in development for Android. I've got most of it up and running, but have just noticed a bug, that I can't always replicate, which (as you know) makes it a nightmare to debug! I'm sure its a logic problem, but I've been staring at it for so long I can't see it. This is the code that sorts the arrays:

    // RANDOMISE UP SOME LETTERS //
    for(int i=0; i<MAX_LETTERS; i++)
    {
        int r = rand.nextInt(25);       

        // SAVE THIS LETTER //
        lettersToUse[i] = letters[r];           
    }       

    // NOW MAKE SURE WE COPY IN OUR WORD //
    for(int i=0; i<nameLen; i++)
    {
        int r = rand.nextInt(MAX_LETTERS);

        Letter tmpLetter = new Letter();
        tmpLetter = letters[lettersInName[i]];                      

        while(in_array(lastElementsUsed, r))
        {
            r = rand.nextInt(MAX_LETTERS);
        }

        lastElementsUsed[i] = r;            

        if(!in_array(lettersToUse, tmpLetter.getLetter()))
        {               
            lettersToUse[r] = tmpLetter;
        }
    }

I've got an array of 18 allowed letters (in the app). The first loop (obviously) just picks a load of random letters. The second loop, then ensures that at least one letter of the word to be guessed is included in the final 18 letters.

The trouble is: Most of the time it works flawlessly. At seemingly random intervals, the final array will be missing a letter from the word to be guessed. It's not always in the same place in the word either.

Can anyone see a problem with my logic? I'm happy to give more information and code, if I've missed a vital piece of the puzzle!

TIA.

Answer 1

This method seems a lot simpler:

for (int i=0; i<(MAX_LETTERS-wordLength); i++)
{
    int r = rand.nextInt(25);       

    // SAVE THIS RANDOM LETTER //
    lettersToUse[i] = letters[r];           
}   
for (int i=MAX_LETTERS-wordLength; i<MAX_LETTERS; i++)
{
    // SAVE THIS LETTER OF THE WORD //
    lettersToUse[i] = lettersInName[r]; //I think that lettersInName is the right variable name to use, hopefully you understand what I'm trying to do here           
}   
lettersToUse.shuffle() //or similar method for whatever array type you're using

Which then ensures you have your word plus the rest of the 18 are filled with random ones, and they've been shuffled