vector how find first and last current value - c++

Question

Task: find first and last current values.
Example:
vector = {1,2,3,1,6,2,1};
need value 1 =>
first index = 0, last = 6; (index/position);
vector<int>::iterator it = find(v.begin(), v.end(), 1);
if (it != v.end())
{
cout << "Element Found" << std::endl;
// Get index of element from iterator
int index = distance(v.begin(), it);
int lastindex = distance(v.end(), it); // bad try to find
cout <<"Index of first element in vector : "<<index<<" last elem ";
// bad code <<lastindex - index <<endl;
}
else
{
cout << "Element Not Found" << std::endl;
}
I found first position but, I can't find last position.
Need help)

Answer 1

You can use reverse iterator to find the last element as follows:
DEMO
int main()
{
std::vector<int> v = {1,2,3,1,6,2,1};
const int currentVal = 1;
const auto itf = std::find(v.cbegin(), v.cend(), currentVal);
const auto itb = std::find(v.crbegin(), v.crend(), currentVal);
if(itf != v.cend()){
std::cout << "front pos: " << std::distance(v.cbegin(), itf) << std::endl;
std::cout << "back pos : " << (v.size() - std::distance(v.crbegin(), itb) - 1) << std::endl;
}
else{
std::cout << currentVal << " is not found." << std::endl;
}
return 0;
}

Answer 2

You can use "rbegin" and "rend" to reverse the list and find the last occurrence by using the same code you have now.
vector = {1,2,3,1,6,2,1};
need value 1 =>
first index = 0, last = 6; (index/position);
vector<int>::iterator it = find(v.begin(), v.end(), 1);
vector<int>::iterator it_reverse = find(v.rbegin(), v.rend(),1);
if (it != v.end() && it_reverse != v.rend())
{
cout << "Element Found" << std::endl;
// Get index of element from iterator
int index = distance(v.begin(), it);
int lastindex = distance(v.rend(), it_reverse); // bad try to find
cout <<"Index of first element in vector : "<<index<<" last elem ";
}
else
{
cout << "Element Not Found" << std::endl;
}