Selecting specific object in queue ( ie peek +1)

Question

if Peek returns the next object in a queue, is there a method I can use to get a specific object? For example, I want to find the third object in the queue and change one of its values?

right now Im just doing a foreach through the queue which might be the best solution, but I didnt know if there was something special you can use with peek? ie Queue.Peek(2)

Answer 1

If you want to access elements directly (with an O(1) operation), use an array instead of a queue because a queue has a different function (FIFO).

A random access operation on a queue will be O(n) because it needs to iterate over every element in the collection...which in turn makes it sequential access, rather than direct random access.

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Then again, since you're using C#, you can use queue.ElementAt(n) from System.Linq (since Queue implements IEnumerable) but that won't be O(1) i.e. it will still iterate over the elements.

Answer 2

Although this is still O(n), it's certainly easier to read if you use the LINQ extention methods ElementAt() or ElementAtOrDefault(), these are extentions of IEnumerable<T>, which Queue<T> implements.

using System.Linq;

Queue<T> queue = new Queue<T>();
T result; 
result = queue.ElementAt(2);
result = queue.ElementAtOrDefault(2);

Edit If you do go with the other suggestions of converting your Queue to an array just for this operation that you need to decide if the likely sizes of your queue and the distance of the index you'll be looking for from the start of your queue justify the O(n) operation of calling .ToArray(). ElementAt(m), not to mention the space requirements of creating a secondary storage location for it.

Answer 3

foreach through a queue. Kind of a paradox.

However, if you can foreach, it is an IEnumerable, so the usual linq extensions apply:

queue.Skip(1).FirstOrDefault()

or

queue.ElementAt(1)