Undefined symbols for architecture x86_64:
  "_num_steps(int, std::__1::vector<int, std::__1::allocator<int> >, std::__1::vector<std::__1::vector<int, std::__1::allocator<int> >, std::__1::allocator<std::__1::vector<int, std::__1::allocator<int> > > >, std::__1::vector<std::__1::vector<int, std::__1::allocator<int> >, std::__1::allocator<std::__1::vector<int, std::__1::allocator<int> > > >)", referenced from:
  num_steps(int, std::__1::vector<int, std::__1::allocator<int> >) in num_steps-FTVSiK.o
 ld: symbol(s) not found for architecture x86_64

#include <iostream>
 #include <vector>
 #include <string>
 #include <cmath>
 
 using namespace std;
 
 //prototypes
 void _num_steps(int amount, vector<int> possible_steps, vector<vector<int>> steps_list, vector<vector<int>> result);
 int sum(vector<int> steps_list);
 void num_steps(int amount, vector<int> possible_steps);
 //
 //
 // 
 
 
 void num_steps(int amount, vector<int> possible_steps) {
  vector<vector<int>> result;
  _num_steps(amount, possible_steps, {{}}, result);
  //print_result(result);
 }
 
 
 int sum(vector<int> steps_list) {
  int sum_of_steps(0);
  for (auto step: steps_list) {
  sum_of_steps += step;
  }
  return sum_of_steps;
 }
 
 void _num_steps(int amount, vector<int> possible_steps, vector<int> steps_list, vector<vector<int>> result) {
  if (sum(steps_list) == amount) {
  result.push_back(steps_list);
  return;
  } 
  else if (sum(steps_list) >= amount) {
  return; 
  }
  for (auto steps: possible_steps) {
  auto steps_list_copy = steps_list;
  steps_list_copy.push_back(steps);
  _num_steps(amount, possible_steps, steps_list_copy, result);
  }
  cout << "yeah" << endl;
  return;
 }
 
 
 int main(int argc, char* argv[]) {
  num_steps(5, {1, 2, 3});
  return 0;
 }