CareerCup

Since you specifically mention a unix file system, you will probably get bonus points for a one line terminal solution before designing a program.

grep -o -w '\w\{4\}' /usr/share/dict/words | sort --random-sort | head -n 1

or

grep -o -w '\w\{4\}' /usr/share/dict/words | shuf -n 1

would work

Assuming the file is sorted with longer length words appearing after shorter one.

Do binary/interpolation search for aaaa and zzzz.

The positions between those two locations are in effect an array of the 4 letter words. (5 bytes each, assuming this is ascii file, with newline after each word)

The positions will tell you how many 4 letter words are there . Say that is W.

Now you can pick a random number in 1 to W. And pick the corresponding word.

This will issue very few reads (and seeks) on the file.

All these unix command line based ideas are great, but if we're asked not to use these but to think of an algorithm and print it out, would reservoir sampling be a good fit?

If you collect all the words in array, then you can generate random number and pick the word using array[randomnumber].

Looks need more details on this question.

maximum number of 4letter words can be 26^4=456,976 ,working on a 32 bit or 64 bit domain we can simply produce a garbage value to cover this range and cm with the random word provided we have got a sub array of 4-letter words from the file

sed -n '/^[a-zA-Z]\{4\}$/p' /usr/share/dict/words

They are probably testing your ability to use preexisting tools! If you are reinventing
the wheel then you waste man hours, unproductive.

str = "/usr/share/dict/words"
  r_str = ""
  while r_str.size < 4 do
    c = str[rand(str.size)]
    r_str += c if c != "/"
  end

;)

public class GenerateRandom {

public static void main(String args[]){
String s="/usr/share/dict/words:";
String word="";
int l=s.length();
List shuffledList= new ArrayList();
for(int i = 0; i < l; i++)
shuffledList.add(s.charAt(i));
Collections.shuffle(shuffledList);
List newList=shuffledList.subList(0, 4);
for(Object i:newList)
word+=i;
System.out.println("The new word is "+word);
}
}

It says generate "a 4 letter word" not all. It seems like most of the answers read the whole file and parse the whole file which seems kind of brute force. Here is a python version that reads 3 orders of magnitude less of the file:

#!/usr/bin/python

import random
import os

CHUNK_SIZE  = 1024


def random_word( wlen ):
    wfile = open('/etc/dictionaries-common/words','r')
    flen = os.stat('/etc/dictionaries-common/words').st_size
    chunks = flen / CHUNK_SIZE
    word = None
    # We might have to try a couple times if we get a chunk that does
    # not have any words of our requested length.
    while not word:
        rpos = random.randint(0,chunks) * CHUNK_SIZE        
        wfile.seek(rpos)
        buf = wfile.read(CHUNK_SIZE)
        # We skip the first and last word because the seeks and read
        # may have left partial words on the ends.
        words = [x  for x in buf.split("\n")[1:-1] if len(x) == wlen ]
        if words:
            p = random.randint(0,len(words)-1)
            word = words[p]

    return word


print random_word(4)