c++ - Removing multiple elements from stl list while iterating -

this not similar can remove elements std::list while iterating through it?. mine different scenario.

lets have list this.

1  2  3  1  2  2  1  3 

i want iterate stl list in such way when first encounter element x activity , need remove elements x in list , continue iterating. whats efficient way of doing in c++.

i worried when remove or erase invalidating iterators. if 1 element potentially increment iterator , erase. in scenario need delete/erase occurances.

was thinking this

while (!list.empty()) {    int num = list.front();    // activity , if successfull    list.remove(num);    } 

dont know if best.

save set of seen numbers , if encounter number in set ignore it. can follows:

list<int> old_list = {1, 2, 3, 1, 2, 2, 1, 3}; list<int> new_list; set<int> seen_elements; for(int el : old_list) {   if (seen_elements.find(el) == seen_elements.end()) {     seen_elements.insert(el);     new_list.push_back(el);   } } return new_list; 

this process each value once , new_list contain first copy of each element in old_list. runs in o(n*log(n)) because each iteration performs set lookup (you can make o(n) using hashset). better o(n^2) approach runs in.