题目:给定一个String类型的大数(非负整数),不能直接转化为Integer,类似如下要求
- The numbers can be arbitrarily large and are non-negative.
- Converting the input string to integer is NOT allowed.
- You should NOT use internal library such as BigInteger.
求0到该数的随机数,例如:给定的数是999,保证0至999中间任意一个数被取到的概率都是1/999