Question

The below code is list element.

List <string> lsLinks = new List<string>();

Before adding new strings i want to check whether list is containing the string i am going to add or not. How can i do that with most efficient way.

I can iterate through whole list and check but i think that would not be performance wise.

Answer 1

The most efficient way would be to simply use a HashSet<T>, either instead of the list (if order doesn’t matter), or in addition to the list, if it does.

i.e. either

HashSet<string> lsLinks = new HashSet<string>();
// now just Add() all you like; only ever one of each, but order is not defined

or

List<string> lsLinks = new List<string>();
HashSet<string> unique = new HashSet<string>();
// now, when needed, check if the item is new to "unique"
if(unique.Add(newValue)) lsLinks.Add(newValue);

You might also find a use for .Distinct() in LINQ, i.e.

var uniqueList = someSourse.Distinct().ToList();