How to iterate map<int, vector <int>>?

Question

I have map<int, vector > like this:

#include <iostream>
#include <map>
#include <vector>

using namespace std;

int main() {
    
    map<int, vector <int>> someMap;
    someMap[5] = {5, 2, 3, 7};
    someMap[151] = {5, 9, 20};

    return 0;
}

I need to find the last vector element in each map value. Output must be like this:

7
20

Thanks :)

Answer 1

You can use the std::vector::back member function as shown below:

#include <iostream>
#include <map>
#include <vector>
#include <cassert>
using namespace std;

int main() {
    
    map<int, vector <int>> someMap;
    someMap[5] = {5, 2, 3, 7};
    someMap[151] = {5, 9, 20};
    //iterate through each element of the map
    for(const std::pair<int, std::vector<int>> &myPair: someMap)
    {
        //make sure the vector is not empty
        assert(!myPair.second.empty());
        
        //print the last element in the vector
        std::cout << myPair.second.back() <<std::endl;
    }
    return 0;
}

The output of the above program is:

7
20

which can be seen here.