Implementing union operation for two sets given as arrays

Question

I need to create a union array of two sets, given as C-arrays. This is what I have so far. I think my if condition is correct, but the output only print out one set of that array. Can you point out what I did wrong?

#include "union_intersection.h"
#include <iostream>
using namespace std;


template <typename T>
void Union(T* left,   int left_size,
           T* right,  int right_size,
           T* result, int& result_size)
{
    
    int i=0, j=0;
    while (i< left_size && j <right_size){
        if (left < right)
        {
            result = left;
            cout<< *result<< "\t";
            i++;
            left++;
            result_size++;
        }
        else if (right<left)
        {
            result =right;
            cout<< *result << "\t";
            j++;
            right++;
            result_size++;
        }
        else
        {
           result =left;
           cout<< *result <<"\t";
           i++; j++;
           left++;
           right++;
           result_size++;
        }

    }
    
}

Answer 1

• You are comparing pointers, not what are pointed at.
• When it reaches at the end of one array, contents of the other arrays will be ignored because the condition in while requires that both array have some elements left.

Try this:

#include "union_intersection.h"
#include <iostream>
using namespace std;


template <typename T>
void Union(T* left, int left_size, T* right,
               int right_size, T* result, int& result_size)
{
    
    int i=0, j=0;
    while (i< left_size || j <right_size){ // change condition to "at least one array have unprocessed elements"
        if (j >= right_size || *left < *right) // compare what is pointed at, and add condition "reached at end of one array"
        {
            result = left;
            cout<< *result<< "\t";
            i++;
            left++;
            result_size++;
        }
        else if (i >= left_size || *right<*left) // compare what is pointed at, and add condition "reached at end of one array"
        {
            result =right;
            cout<< *result << "\t";
            j++;
            right++;
            result_size++;
        }
        else
        {
            result =left;
            cout<< *result <<"\t";
           i++; j++;
           left++;
           right++;
           result_size++;
        }

    }
    
}

Also it looks weird that the value of the argument result is ignored and used as simple local variable, but I don't think this is invalid because the question only says about printing out and there are no specifications about what should be written or read to/from what is pointed at by result.

Answer 2

With @MikeCat help, below is my finish function. I also include the loop to print out the remaining element.

template <typename T>
void Union(T* left, int left_size, T* right,
               int right_size, T* result, int& result_size)
{

    int i=0, j=0;
    while (i< left_size && j <right_size){
        if (*left < *right || j >=right_size)
        {
            result = left;
            cout<< *result<< "\t";
            i++;
            left++;
            result_size++;
        }
        else if (*right<*left || i>= left_size)
        {
            result =right;
            cout<< *result << "\t";
            j++;
            right++;
            result_size++;
        }
        else
        {
            result =left;
            cout<< *result <<"\t";
           i++; j++;
           left++;
           right++;
           result_size++;
        }

    }
    while (i < left_size)
    {
        cout<< *left<< "\t";
        left++;
        ++i;
        result_size++;
    }
    while (j < right_size)
    {
        cout<< *right<< "\t";
        ++j;
        right++;
        result_size++;
    }

}