Simultaneous Union and Intersection between two maps in C++

Question

While doing a college project I came upon the following problem: I have two maps (Kmer1 and Kmer2) which are composed by a string(key) and a int(value). I have to calculate the distance which follows this formula

[1-(I/U)]*100

Where...
     ...U = the sum of all int values inside Kmer1 U Kmer2
     ...I = the sum of all int values inside Kmer1 ∩ Kmer2

Consider that...
             ... The U and ∩ are made evaluating the keys (strings)
             ... When an element is in both maps:
                 - At the Union we add the one with higher int value
                 - At the Intersection we add the one with lower int value

Example:

Kmer1 = AAB¹ AAC¹ AAG³
Kmer2 = AAG¹ AAT² ABB¹

Union = AAB¹ AAC¹ AAG³ AAT² ABB¹   U= 8
Intersection = AAG¹                I= 1
Distance = 87.5

Code time! I've been trying to solve it but all solutions are like.. partially right, not all cases are covered. So when I tried to cover them, I ended in infinite loops, exceptions rising, long long nests of if-else (which were awfull..) anyway, here is the the least worse and non working try:

The setup:

Species::Kmer Kmer1, Kmer2;        //The two following lines get the Kmer from another
Kmer1 = esp1->second.query_kmer(); //object.
Kmer2 = esp2->second.query_kmer(); 

Species::Kmer::const_iterator it1, it2, last1, last2;
it1 = Kmer1.cbegin();           //Both Kmer are maps, therefore they are ordered and
it2 = Kmer2.cbegin();           //whitout duplicates.
last1 = --Kmer1.cend();
last2 = --Kmer2.cend();

double U, I;
U = I = 0;

The loop where the formula is applied:

while (it1 != Kmer1.cend() and it2 != Kmer2.cend()){
    if (it1->first == it2->first) {         
        if (it1->second > it2->second) {
            U += it1->second;
            I += it2->second;
        } else {
            U += it2->second;
            I += it1->second;
        }
        ++it1;
        ++it2;

    } else if (it1->first < it2->first) {
        U += it1->second;
        ++it1;
    } else {
        U += it2->second;
        ++it2;
    }
}

Note that instead of first creating the Union and the intersection and then doing the total sum of each, I jumped directly to the sum of the values. I know maybe it's not that hard but I've been trying to solve it but I'm pretty much stuck...

---

I've uploaded the whole code at Github: (Maybe it helps)
    - There is a makefile to build the code
    - There is a file called input.txt with a sample for this specific problem
    - Also inside the input.txt, after line13 (fin) I've added the expected output
    - Executing ./program.exe < input.txt should be enough to test it.

https://github.com/PauGalopa/Cpp-Micro-Projects/tree/master/Release

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IMPORTANT Yes! I'm aware of almost all the STL functionality that could do this in a few lines BUT... Since this is a college project i'm bound to the limitations of the sillabus so consider that I'm only allowed to use "map" "string" "vector" and a few more. No, I can't use "algorithm" (I really wish I could) I'll clarify any doubt about which things I can do or use in the coments.

Answer 1

Add these two loops just after your main while loop.

while (it1 != Kmer1.cend()){
    U += it1->second;
    it1++;
}
while (it2 != Kmer2.cend()){
    U += it2->second;
    it2++;
}