What is the queue equivalent of POP ?

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Java

import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.Stack;

public class QS {
	 public static void main(String[] args) {
	        Scanner scan = new Scanner(System.in);
	        String input = scan.nextLine();
	        scan.close();
	char[] s = input.toCharArray();
	PriorityQueue<Character> queue=new PriorityQueue<Character>();
    Stack<Character> st = new Stack<Character>();
    for (char c : s) {
        st.push(c);
        queue.add(c);
    }
    System.out.println("STACK .... ");
    for(int i =0;i<input.length();i++){
    	System.out.println(st.pop());
    }
    System.out.println("QUEUE .... ");
    for(int i =0;i<input.length();i++){
    System.out.println(queue.poll());
    } 
    }
}

What I have tried:

I/O :

racecar
STACK ....
r
a
c
e
c
a
r
QUEUE ....
a
a
c
c
e
r
r

I am looking for "racecar" as output from the queue too.. Where am I going wrong ?

Posted 26-Oct-16 20:58pm

GaneshRfromSpace

Updated 26-Oct-16 21:01pm

v3

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CPallini · Accepted Answer · 2016-10-26T21:17:00

You chose the wrong implementing class, the priority queue, well, prioritizes some inputs with respect others (in your case uses alphabetic order as priority criterion).
Using, for instance the LinkedList implementing class, you could obtain the expected output:

Java

import java.util.LinkedList;
import java.util.Scanner;
import java.util.Stack;

public class QS {
   public static void main(String[] args) {
          Scanner scan = new Scanner(System.in);
          String input = scan.nextLine();
          scan.close();
  char[] s = input.toCharArray();
  LinkedList<Character> queue=new LinkedList<Character>();
    Stack<Character> st = new Stack<Character>();
    for (char c : s) {
        st.push(c);
        queue.add(c);
    }
    System.out.println("STACK .... ");
    for(int i =0;i<input.length();i++){
      System.out.println(st.pop());
    }
    System.out.println("QUEUE .... ");
    for(int i =0;i<input.length();i++){
    System.out.println(queue.poll());
    }
    }
}