Question

Using ONLY the following header functions:

#include "cmpt_error.h"
#include <iostream>
#include <string>
#include <vector>
#include <cassert>
using namespace std;

Create a C++ function that satisfies the condition using recursion, NO WHILE OR FOR LOOPS.

Pre-condition:
     a.size() == b.size(), and a.size() > 0
Post-condition:
     Returns a vector equal to {min(a[0],b[0]), min(a[1],b[1]),
     min(a[2],b[2]), ..., min(a[n],b[n])}, where n == a.size().

For example, min_vec({3, 4, 1}, {2, 5, 2}) returns the new vector {2, 4, 1}.

These are the function headers:

vector<int> min_vec(const vector<int>& a, const vector<int>& b);
void min_vec_test();

Answer 1

Code:

//helper function

void help_min_vec(const vector<int>& a, const vector<int>& b,vector <int>& c,int idx)
{
   if(idx>=a.size()) return;
   c.push_back(min(a[idx],b[idx]));
   return help_min_vec(a,b,c,idx+1);
}
vector<int> min_vec(const vector<int>& a, const vector<int>& b)
{
   vector <int> c;
   help_min_vec(a,b,c,0);
   return c;
}
void min_vec_test(){
   cout<<"Testing min_vec... ";
   assert((min_vec({1},{2})== vector <int> {1}));
   assert((min_vec({1,10},{5,2}) == vector <int> {1,2} ));
   assert((min_vec({3,4,1},{2,5,2})== vector <int> {2,4,1}));
   cout<<"all min_vec tests passed!\n";
}

===========

I have tested it using :

Output:

=========

Since we are creating vectors using extended intializers use c++11 or above to run the code.

min_vec() functions calls another helper function help_min_vec() which takes four arguments. The first three are vector and last one is int. The purpose of variable idx is to maintain check on which element we have reached and push the current minimum value for that index. After that it is incremented and recursive call is made thus avoiding the use of the loops. The testing function uses assert() to check the min_vec() function returned output.

Please comment if you don't understand any part of code.