CODEWITHSUNDEEP
javaqueue
Lost2
Lost2

Reputation: 148

How to get the position of a element in a Queue

Is there a simpel way to get the current position of a element in a Queue for example:

My current queue is [1,0,5,4,7,8,6]

i want to know the position of the 4 in this queue, in this exampel its 3, is there a way to achieve this with the java queue?

Upvotes: 0

Views: 8941

Answers (5)

JamesB
JamesB

Reputation: 529

String value = "Value";
Queue<String> queueList= new LinkedList<>();
List listQueue= new ArrayList(queueList);

System.out.println("Index of : " + lista.indexOf("Value"));

Upvotes: 0

Ben
Ben

Reputation: 27

Queue may not be the best solution as it doesn't store an index. However, queue implements Iterable so you could iterate over the structure:

    Queue<Integer> queue = new LinkedList<>();

    queue.add(1);
    queue.add(0);
    queue.add(5);
    queue.add(4);
    queue.add(7);
    queue.add(8);
    queue.add(6);

    int lookingFor = 0;

    int counter = 0;
    for (Integer number : queue) {
        if (number == lookingFor) {
            System.out.println(lookingFor + " is at position " + counter + " in the queue.");
            break;
        }
        else counter++;
    }

This will output the following:

0 is at position 1 in the queue.

Note this will find the first occurrence of 0 only.

Upvotes: 3

Hearen
Hearen

Reputation: 7838

As you already knew that queue is a collection that gives us FIFO by adding (to the last) and polling (from the head/first).

Which it also means there is no guarantee that you can use it to locate its index/position in the queue.

If you really need something like that, instead you can try List to achieve the same effect as follows using add(E e) and remove(0) and indexOf(Object o):

public static void main(String... args) {
    List<Integer> list = new ArrayList<>();
    int[] arr = new int[]{1,0,5,4,7,8,6};
    for (int a : arr) {
        list.add(a);
    }
    System.out.println("After adding: " + list);
    System.out.println(list.indexOf(4));
    System.out.print("Popping out now: ");
    while(!list.isEmpty()) {
        System.out.print(list.remove(0) + " ");
    }
}

And the result will be:

After adding: [1, 0, 5, 4, 7, 8, 6]
3 // you can find the index easily;
Popping out now: 1 0 5 4 7 8 6 // still FIFO;

Upvotes: 1

TheCrimsonSpace
TheCrimsonSpace

Reputation: 188

The default interface of Queue does not have any methods for this. If you need this functionality I think you'll have to create your own implementation of the interface using an indexed collection under the hood.

Upvotes: 1

InExperience
InExperience

Reputation: 103

it supports FIFO, and size() you can't have the index of it. You have to count the remove actions on the pile.

Upvotes: 0

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