Find if std::list contains element from another std::list

Question

I have two lists:

std::list<MyClass1> listClass1;
std::list<MyClass2> listClass2;

For sake of simplicity lets say that they have these elements:

listClass1

{id: 1, name: "Test1"}
{id: 2, name: "Test2"}
{id: 3, name: "Test3"}
{id: 4, name: "Test4"}
{id: 5, name: "Test5"}

listClass2

{id: 1, name: "Test2"}
{id: 2, name: "Test5"}

I need to find out if listClass2 name property is in listClass1 name . I mean, if they match. Otherwise return an error or -1.

Is there a more efficient way than looping twice? That's all I could think of at the moment, so any help is appreciated.

Answer 1

You can store one (larger of the two would be better) of the list's names into a set<string> and iterate over the other list and see if the set contains that element.

That should reduce your running time from O(m * n) to O(m * log(n)).

PS: I believe using a hash table can further reduce that log(n) factor.