For the very same Word Racer clone I had to write a grid randomizer that would be able to customize the frequency of vowels, a max instance count for each vowel, consonant and special character ( less frequently word encountered consonants ).

Sounds complicated ? Let's see

// precalcs

charsToGenerate  = x;
vowelFrequency   = [0.0 - 1.0]
neededVowels     = charsToGenerate * vowelFrequency
neededConsonants = charsToGenerate - neededVowels

// iteration

for ( i = 0; i < charsToGenerate; i++ ) {
    randomLetter = GetRandomChar();
}


// selectors


char GetRandomChar() {
    if ( neededVowels > 0 && neededConsonants > 0) {
        if ( rand() & 1 ) {
            return chooseVowel();
        } else {
            return chooseConsonant();
        }
    } else {
        if ( neededConsonants > 0 ) {
            return chooseConsonant();
        } else {
            return chooseVowel();
        }
    }
}


char chooseVowel() {
    select random vowel
    while ( vowel's InstanceCount >= maxVowelInstanceCount ) {
        select random vowel
    }

    increment vowel's InstanceCount
    neededVowels--

    return vowel
}


char chooseConsonant() {
    select random consonant
    done = false
    while ( !done ) {
        if ( IsSpecialChar( consonant ) ) {
            if ( instanceCount < maxSpecialCharInstanceCount ) {
                done = true
            } else {
                select random consonant
            }
        } else {
            if ( instanceCount < maxConsonantInstanceCount ) {
                done = true
            } else {
                select random consonant
            }
        }
    }

    increment consonant's InstanceCount
    neededConsonants--

    return consonant
}

Of course this code won't compile. Of course there may be better ways of doing it. Of course I hate pure pseudocode.

You will have to watch a particular case which could generate an infinite loop which occurs when