Find vector element in second vector

Question

Given two vectors of integers, how to determinate if there's some element from 1st vector is present in 2nd one?

Answer 1

You could take the set_intersection of both vectors, and then check if the resulting intersection is empty:

std::sort(v1.begin(), v1.end());
std::sort(v2.begin(), v2.end());
std::set_intersection(v1.begin()
  , v1.end()
  , v2.begin()
  , v2.end()
  , std::back_inserter(v3));
bool containsElements = !v3.empty();

set_intersection can be found in #include <algorithm>

For set_intersection to work, both vectors must first be sorted.

Answer 2

I guess something like this should work:

std::vector<int> v1,v2;
if(std::find_first_of(v2.begin(),v2.end(),v1.begin(),v1.end()) != v2.end())
   std::cout << "found!\n";

Answer 3

I think something like this:

bool contains(const std::vector<int>& vec, int val){
    for(std::vector<int>::const_iterator it=vec.begin(); it!=vec.end(); ++it){
        if(*it==val){
            return true;
        }
    }
    return false;
}

bool contains(const std::vector<int>& from, const std::vector<int>& in){
    for(std::vector<int>::const_iterator it=from.begin(); it!=from.end(); ++it){
        if(contains(in, *it)){
            return true;
        }
    }
    return false;
}

// Example
std::vector<int> a;
std::vector<int> b;

a.push_back(2);
a.push_back(1);
b.push_back(0);
b.push_back(1);

bool contains = contains(a, b);