Check if element is in the list (contains)
I've got a list of elements, say, integers and I want to check if my variable (another integer) is one of the elements from the list. In python I'd do:
my_list = [1,2,3,4] # elements
my_var = 3 # my variable
my_var in my_list # returns boolean
How to do that in C++? I thought of using std::list
, but I can find no find
method in it. I can see such method in std::set
structure.
More deeply, the problem is that my program is given some unique ids (a list, a set, whatever) and I iterate over a long list of input data (ids) and check if they are included in the list (boolean value returned for each iteration step). And I'm not sure how should I do that in C++.
Solution 1:
You can use std::find
bool found = (std::find(my_list.begin(), my_list.end(), my_var) != my_list.end());
You need to include <algorithm>
. It should work on standard containers, vectors lists, etc...
Solution 2:
std::list
does not provide a search method. You can iterate over the list and check if the element exists or use std::find
. But I think for your situation std::set
is more preferable. The former will take O(n)
time but later will take O(lg(n))
time to search.
You can simply use:
int my_var = 3;
std::set<int> mySet {1, 2, 3, 4};
if(mySet.find(myVar) != mySet.end()){
//do whatever
}