getRandomTripplet()

/*
  2014-08-29
  bluepp
  May the force be with me!
  
  http://www.mitbbs.com/article_t/JobHunting/32764727.html
  
  Given a function 

getRandomTripplet() 

which returns a random triplet of letters from a string. You don't know the 
string using calls to this function you have to correctly guess the string. 
the length of the string is also given. 

Lets say the string is helloworld the function getRandomTriplet will return 
things like 

hlo 
hew 
wld 
owo 

the function maintains the relative order of the letters. so it will never 
return 

ohl since h is before o in the string. 
owe since w is after e 

The string is not known you are only given length of the string.


据说是FB的phone interview

------------------

给你一个password 假定6位， 
有个function 每call 一次就给你一个triplet 是password 里的随即三位，order不变
。比如google, 可能返回， ggl, goe, oog, ool, ........
问如何最有效破译这个密码，写code.