Question

USING C++:

Write a function that will return the number of elements that appear in pairs in a vector (i.e., the number of elements that appear exactly twice).

E.g. if the vector v={1,3,7,10,1,1,3,5,10,5}, the function will return 3 (since 3, 5 and 10 appear in pairs)

The function prototype is given below:

template <class T>
int pairCount(const vector<T>&);

Answer 1

#include <iostream>
#include <vector>

using namespace std;

template<class T>
int pairCount(const vector<T> &);

int main() {
    vector<int> v = {1, 3, 7, 10, 1, 1, 3, 5, 10, 5};
    cout << pairCount(v) << endl;
    return 0;
}

template<class T>
int pairCount(const vector<T> &v) {
    int count = 0;
    for (int i = 0; i < v.size(); ++i) {
        int c = 0;
        for (int j = 0; j < v.size(); ++j) {
            if (v[i] == v[j])
                ++c;
        }
        if (c == 2) {
            ++count;
        }
    }
    return count / 2;
}