Question

2. Given two unsorted STL lists X and P, write a valid C++ function intersection(X, P) that returns a new list that contains the elements common to both X and P. For example, if X = 5, 2, 1, 4 and P = 4, 5, 7; your algorithm should return a new list containing 5 and 4 (order is not important). Also specify the running time of your algorithm using Big-Oh notation. Hint: As the lists are unsorted, a straightforward algorithm would need a double for loop.

Answer 1

$\color{red}\underline{intersection:}$

list<int> intersection(list<int> X, list<int> P)
{
list<int> result;
for (list<int>::iterator i = X.begin(); i != X.end(); i++) {
for (list<int>::iterator j = P.begin(); j != P.end(); j++) {
int n = *i, m = *j;
if (n == m) {
result.push_back(n);
}
}
}
return result;
}

$\color{red}\underline{Time\;Complexity:}$

O(n * Tm