c++ count vector elements
#include <iostream>
#include <vector>
#include <algorithm>
int main() {
std::vector<int> vec = {1, 2, 3, 4, 5, 2, 3, 4, 1, 2, 5};
std::sort(vec.begin(), vec.end());
auto last = std::unique(vec.begin(), vec.end());
int count = std::distance(vec.begin(), last);
std::cout << "Number of unique elements in the vector: " << count << std::endl;
return 0;
}