Suppose you want to make a random 9 digit number, using every number from 1 to 9 exactly once. You have a process called random(top) that gives a random number up to top (if top was 5, it would give random numbers from 1 to 5)

a) How could you do this?

b) If top couldn't be more than 9, how could you do this using random(top) only 9 times (or less)?

struct MyRand {
    typedef std::vector<int>::difference_type DType;

    DType operator()(DType max) {
        return random(max) - 1;
    }
};

int foo() {
    std::vector<int> digits;

    for (int i = 1; i <= 9; ++i)
        digits.push_back(i);

    MyRand myRand;
    std::random_shuffle(digits.begin(), digits.end(), myRand);

    int result(0);

    for (int i = 0; i < 9; ++i)
        result = result * 10 + digits[i];

    return result;
}

Posted by friedlinguini on 2003-05-02 10:28:52