CODEWITHSUNDEEP
c++iteratorcomparestd
NaturalDemon
NaturalDemon

Reputation: 1014

How to keep in sync looping over 2 maps?

how to loop in sync over 2 maps?
it could be that either map1 or map2 contains more keys.
how do i set the preference? and increment the corresponding iterator?

example values of 2 maps:

4 7 10 11 12 13 14 
3 4 7 8 10 11 12 13 14

map1 doesn't contain a '3'

What's the best way to iterate over two or more containers simultaneously

std::map<int, int> map1;
std::map<int, int> map2;
auto itA = begin(map1);
auto itB = begin(map2);

while(itA != end(map1) || itB != end(map2))
{
    if(itA != end(map1))
    {
        ++itA;
    }
    if(itB != end(map2))
    {
        ++itB;
    }
}

using this code would result that you try yo compare 2 unequal numbers / values.
so you must halt incrementing one or the other iterator until both value are equal.

Upvotes: 0

Views: 145

Answers (1)

NaturalDemon
NaturalDemon

Reputation: 1014

i found the answer:

if(map1.first == map2.first){
    if(itA != end(map1)){
        ++itA;
    }
    if(itB != end(map2)){
        ++itB;
    }
}
else if(map1.first < map2.first){
    if(itA != end(map1)){
        ++itA;
    }
}
else if(map1.first > map2.first){
    if(itB != end(map2)){
        ++itB;
    }
}

Upvotes: 1

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