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Accessing map value by index

Using std::advance or std::next

c2 = a2 + b2

define and use

  • aMap and bMap
    std::map<int, string> aMap;
    std::map<int, string> bMap;
  • calc it
    int a = getMapKey(aMap, 0);
    int b = getMapKey(bMap, 0);

getMapKey

int getMapKey(std::map<int, std::string> myMap ,int index) { }

  • next
    auto it = myMap.begin();
    auto it2 = std::next(it, index);
    return it2->first;
  • advance
    auto it = myMap.begin();
    std::advance(it, index);
    return it->first;

diff

std::next std::advance
It is used to return nth successor of an iterator It does not have any return type.
It takes two parameters that are -: number of elements and a iterator. It takes two parameters number of elements and iterator
Its Time complexity in best case is constant Its Time complexity in best case is constant
Its Time complexity in worst case is linear Its Time complexity in worst case is linear

test

#include <iostream>
#include <map>
#include <cmath>

int getMapKey(std::map<int, std::string> myMap ,int index) {
    auto it = myMap.begin();
    auto it2 = std::next(it, index);
    return it2->first;
}

int main() {
    std::map<int, std::string> aMap;
    std::map<int, std::string> bMap;

    aMap.insert(std::pair<int, std::string>(3, "a"));
    bMap.insert(std::pair<int, std::string>(4, "b"));

    int a = getMapKey(aMap, 0);
    int b = getMapKey(bMap, 0);

    int c = pow(a, 2) + pow(b, 2);

    std::cout << sqrt(c) << std::endl;
    return 0;
}

Ref