O(n)时间的排序

void SortAges(int ages[], int length)
{
    if(ages == NULL || length <= 0)
        return;

    const int oldestAge = 99;
    int timesOfAge[oldestAge + 1];

    for(int i = 0; i <= oldestAge; ++ i)
        timesOfAge[i] = 0;

    for(int i = 0; i < length; ++ i)
    {
        int age = ages[i];
        if(age < 0 || age > oldestAge)
            throw new std::exception("age out of range.");

        ++ timesOfAge[age];
    }

    int index = 0;
    for(int i = 0; i <= oldestAge; ++ i)
    {
        for(int j = 0; j < timesOfAge[i]; ++ j)
        {
            ages[index] = i;
            ++ index;
        }
    }
}