Yet another Fibonacci number generator

First attempt at dynamic programming. I want to make this run faster and better.

fibonacci.cpp

#include "fibonacci.h"

std::map initializeMap() {
    std::map m;
    m[0] = 0;
    m[1] = 1;
    return m;
}

std::map __fib_result_map = initializeMap();

unsigned long long int fibonacci(int seq) {
    using namespace std;
    map& m = __fib_result_map;
    if(m[seq] == 0 && seq != 0) {
        m[seq] = fibonacci(seq - 2) + fibonacci(seq - 1);
    }
    return m[seq];
}

fibonacci.h

#ifndef __fibonacci
#define __fibonacci

#include 
#include 
#include 
#include 
#include 

unsigned long long int fibonacci(int seq);

#endif

fib_cpp.cpp

#include "fibonacci.h"
#include 
using namespace std;

int main(int argc, char* argv[]) {

    if(argc \n";
        return 1;
    }
    for(int i = 1; i < argc; i++) {
        cout << fibonacci(atoi(argv[i])) << endl;
    }
    return 0;
}

Here is the repository on Github.

Assuming you're using the current c++ standard, since you don't specify in your question.

• Prefer stoi to atoi. atoi has issues.

• Prefer standard int types: std::uint128_t instead of unsigned long long int

• Create a type alias for your map type since you use it a lot.

• Don't include unnecessary headers in the fibbonacci.h file. Include them in the implementation.

• It would make more sense to implement your memoizing map statically in the function.

• You should use the map count method rather than relying on [] returning zero for a missing key

Putting these together

using fibmap = std::map;

std::uint128_t fibonacci(int seq) {

    static fibmap m = {{0,0}, {0,1}};
    if (!m.count(seq)){
        m[seq] = fibonacci(seq - 2) + fibonacci(seq - 1);
    }
    return m[seq];
}

StackExchange Code Review Q#139888, answer score: 12