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I previously posted a Reservoir-Sampling program, which was basically a test version of this one. This is an assignment. In the code below, I use RunTimeException to control when scanner finishes reading data. Reasons for this being:

I previously posted a Reservoir-Sampling program, which was basically a test version of this one. This is an assignment. In the code below, I use RunTimeException to control when scanner finishes reading data. Reasons for this being:

Edited code:

public class Subset {
    
    public static void main(String[] args) {
        
        int sampleSize = Integer.parseInt(args[0]);
        String[] sample = new String[sampleSize];
        int i = 0;
        // initialize the sample from reservoir
        while(i < sample.length){
            sample[i++] = StdIn.readString(); // StdIn : a class in the provided JAR.
        }
        try{
            for(; ; i++){ 
                int randomIndex = (int)(Math.random()*(i + 1));
                if(randomIndex < sampleSize){
                    sample[randomIndex] = StdIn.readString();
                }
            }
        }catch(RuntimeException e){
            // do nothing
        }       
        for(String s : sample){
            System.out.print(s + " ");
        }
        
    }
}

StdIn.readString():

public static String readString() {
    return scanner.next();
}

Edit: to clear out confusion  , i am posting what the api and the instructor demands.

Subset client. Write a client program Subset.java that takes a command-line integer k, 
reads in a sequence of N strings from standard input using StdIn.readString(), 
and prints out exactly k of them, uniformly at random. Each item from the sequence can be printed out at most once. 
You may assume that k = 0 and no greater than the number of string on standard input.

% echo A B C D E F G H I | java Subset 3       % echo AA BB BB BB BB BB CC CC | java Subset 8
C                                              BB
G                                              AA
A                                              BB
                                               CC
% echo A B C D E F G H I | java Subset 3       BB
E                                              BB
F                                              CC
G                                              BB
Your client should use only constant space plus one object either of type Deque or of type RandomizedQueue;
use generics properly to avoid casting and compiler warnings. It should also use time and space proportional to 
at most N in the worst case, where N is the number of strings on standard input. 
(For an extra challenge, use space proportional to k.) It should have the following API.

public class Subset {
   public static void main(String[] args)
}

import java.io.BufferedInputStream;
import java.util.Scanner;

public class Subset {
    
    public static void main(String[] args) {
        int k = Integer.parseInt(args[0]);
        String[] arr = new String[k];
        int i = 0;
        String str;     
        while((str=stdin.readString())!=null && i < arr.length){
            arr[i++] = str;
            // System.out.println(str);
        }
        try{
            for(; (str=stdin.readString())!=null; i++){
                int r = (int)(Math.random()*(i + 1));
                if(r < k){
                    arr[r] = str;
                    //System.out.println(str);
                }
            }
        }catch(RuntimeException e){ // do nothing }     
        for(String s : arr){
            System.out.print(s + " ");
        }
        System.out.println("\n");
    }
}
class stdin{
    private stdin(){}
    private static Scanner sc = new Scanner(new BufferedInputStream(System.in));
    public static String readString(){
        return sc.next();
    }
}

To clear out confusion, I am posting what the API and the instructor demands:

Subset client. Write a client program Subset.java that takes a command-line integer k, 
reads in a sequence of N strings from standard input using StdIn.readString(), 
and prints out exactly k of them, uniformly at random. Each item from the sequence can be printed out at most once. 
You may assume that k = 0 and no greater than the number of string on standard input.

% echo A B C D E F G H I | java Subset 3       % echo AA BB BB BB BB BB CC CC | java Subset 8
C                                              BB
G                                              AA
A                                              BB
                                               CC
% echo A B C D E F G H I | java Subset 3       BB
E                                              BB
F                                              CC
G                                              BB
Your client should use only constant space plus one object either of type Deque or of type RandomizedQueue;
use generics properly to avoid casting and compiler warnings. It should also use time and space proportional to 
at most N in the worst case, where N is the number of strings on standard input. 
(For an extra challenge, use space proportional to k.) It should have the following API.

public class Subset {
   public static void main(String[] args)
}

Edit: to clear out confusion , i am posting what the api and the instructor demands.

Subset client. Write a client program Subset.java that takes a command-line integer k, 
reads in a sequence of N strings from standard input using StdIn.readString(), 
and prints out exactly k of them, uniformly at random. Each item from the sequence can be printed out at most once. 
You may assume that k = 0 and no greater than the number of string on standard input.

% echo A B C D E F G H I | java Subset 3       % echo AA BB BB BB BB BB CC CC | java Subset 8
C                                              BB
G                                              AA
A                                              BB
                                               CC
% echo A B C D E F G H I | java Subset 3       BB
E                                              BB
F                                              CC
G                                              BB
Your client should use only constant space plus one object either of type Deque or of type RandomizedQueue;
use generics properly to avoid casting and compiler warnings. It should also use time and space proportional to 
at most N in the worst case, where N is the number of strings on standard input. 
(For an extra challenge, use space proportional to k.) It should have the following API.

public class Subset {
   public static void main(String[] args)
}