universalShuffleAlgorithm.sol

    // The shuffle algorithm is similar to Algorithm P (Shuffle) from Knuth, 1969, in turn similar to the Fisher–Yates shuffle 
    // from 1938. It gets the position of an object from shufflingIndex, using a random number generator, and then updates the 
    // index so that the same position cannot be given to  another object, and does so by switching places between the object 
    // that was picked, and the first object in the list, exchange shufflingIndex[randomNumber] and shufflingIndex[counter].

    struct ShuffleAlgorithm {
        mapping(uint => uint) shufflingIndex;
        uint counter;
    }
    ShuffleAlgorithm shuffleUtility;
    mapping(address => uint) userID;
    uint totalPopulation;

    function pickFromHat() {
        shuffleUtility.counter++;
        entropy = generateRandomNumber(entropy);
        uint randomNumber = 1 + (entropy % (totalPopulation - shuffleUtility.counter));
        uint randomPosition = shuffleUtility.counter + randomNumber;
        if(shuffleUtility.shufflingIndex[randomPosition] == 0) shuffleUtility.shufflingIndex[randomPosition] = randomPosition;
        if(shuffleUtility.shufflingIndex[shuffleUtility.counter] == 0) shuffleUtility.shufflingIndex[shuffleUtility.counter] = shuffleUtility.counter;
        shuffleUtility.shufflingIndex[randomPosition] = shuffleUtility.shufflingIndex[shuffleUtility.counter];
        shuffleUtility.shufflingIndex[shuffleUtility.counter] = shuffleUtility.shufflingIndex[randomPosition];
    }