I have two sorted lists as below:

``var list1 = new List<int>() { 1, 1, 1, 2, 3 };var list2 = new List<int>() { 1, 1, 2, 2, 4 };``

I want the output to be: `{1, 1, 2}`

How to do this in C#?

Is there a way using Linq?

The extra 1 means you can't use `Intersect` because it returns a set.

Here's some code that does what you need:

``````var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };

var grouped1 =
from n in list1
group n by n
into g
select new {g.Key, Count = g.Count()};

var grouped2 =
from n in list2
group n by n
into g
select new {g.Key, Count = g.Count()};

var joined =
from b in grouped2
join a in grouped1 on b.Key equals a.Key
select new {b.Key, Count = Math.Min(b.Count, a.Count)};

var result = joined.SelectMany(a => Enumerable.Repeat(a.Key, a.Count));

CollectionAssert.AreEquivalent(new[] {1, 1, 2}, result);
``````

Use `Intersect`:

`````` var commonElements = list1.Intersect(list2).ToList();
``````

I am late in answering this question, this might help future visitors.

``````            List<int> p = new List<int> { 1, 1, 1, 2, 3 };
List<int> q = new List<int> { 1, 1, 2, 2, 4 };
List<int> x = new List<int>();
for (int i = 0; i < p.Count; i++ )
{
if (p[i] == q[i])
{
}
}
``````

This works nicely:

``````var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };

var lookup1 = list1.ToLookup(x => x);
var lookup2 = list2.ToLookup(x => x);

var results = lookup1.SelectMany(l1s => lookup2[l1s.Key].Zip(l1s, (l2, l1) => l1));
``````

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