Generate randN from rand1

https://sites.google.com/site/codingbughunter/algorithm-question-discuss

You have a function rand1() to random generate number 0 or 1. Can you make a function to generate randN(int n)

 给定rand1()：能够产生random数字0,1
    用rand1()实现:
    rand3()--> 0, 1, 2, 3
    rand4()--> 0, 1, 2, 3, 4
    randN(int n)--> 0, 1, ..., N      n可以是任意整数，包括0、负整数、正整数
，注意edge case


 public int randomGenerateNum(int n){
  int numOfDigits = 0;
  int booleanNum = (n<0 ? 1: 0);
  
   n = Math.abs(n);
   int tmp = n;
  while(tmp > 0){
   numOfDigits++;
   tmp /= 2;
  }
  
  
  int res = 0;
  
  while(true){
   for(int i = 0; i<numOfDigits; i++){
    res = res*2+rand1();
   }
   if(res <= n){
    break;
   }else{
    res = 0;
   }
  }
  
  return booleanNum == 0 ? res : -res;
  
 }
 
 private int rand1(){ // for test
  Random rn = new Random();
  return rn.nextInt(2);
 }