Question

Write the algorithm for this program using the C++ language (not python or java). The explanation needs to be at least 250 words. Explain everything throughly step by step.

While there is a built-in pop_back function in the vector class, there is no built-in pop_front function. Suppose a program needs a pop_front function that will remove the first element from the vector. For example, if the original vector is [1, 2, 3, 4, 5], then after passing in this vector to pop_front the new resulting vector will be [2, 3, 4, 5]. As another example, if the original vector is [1, 2], then the new resulting vector after calling pop_front will be [2]. The function also needs to properly handle the case where the vector is already empty.

you don't have to implement the code for this function, but you do need to think about a general algorithm that can be used to correctly remove the first element from ANY vector that is passed to the function (make sure to handle the case where the vector is already empty).

Then thoroughly describe in detail your algorithm for the vector pop_front function. In particular, make sure to describe things such as (1) what your parameter list for the function would look like, (2) how your looping structure will work, and (3) how you will handle the case where the vector is already empty.

Answer 1

Algorithm:

we have a begin function in a vector which returns the iterator pointing to the first element.

We have another method called as erase, which takes the position of the element to be removed in the form of the iterator.

So if we pass the iterator returned by the begin() to the erase() method, then the first element will be removed from the vector.

We erase the first element of the vector only in case if the vector size is greater than 0 i.e. vector is not empty.

(1) what your parameter list for the function would look like

Parameter is reference of the vector which we are required to remove the first element.

(2) how your looping structure will work

  No looping is required, if the vector is not empty, we get the iterator pointing to the first element using begin() and then we pass this to erase() function which removes the first element of the vector in question

(3) how you will handle the case where the vector is already empty.

Just throw a message saying that vector is empty and do nothing.

Below is the C++ code for your reference:

#include <iostream>
#include <vector>

template<typename T>
void pop_front(std::vector<T> &v)
{
   if (v.size() > 0) {
       v.erase(v.begin());
   }

   else{
   std::cout<<"vector is empty";
   }
}

int main()
{
   std::vector<int> nums = { 1, 2, 3, 4, 5 };
   pop_front(nums);

   for (int i: nums)
       std::cout << i << ' ';
   std::cout<<"\n";
   std::vector<int> nums2 = { 1, 2 };
   pop_front(nums2);

   for (int i: nums2)
       std::cout << i << ' ';

   return 0;
}