Sort a string array in Alphabetical Order - C++ 11

Question

I'm preparing for an interview and while looking across candidate experiences i came across the following question -

Given an array of strings : { “Sdjksajd”, “Skjdasjj”, “Bjsdakja”, “Xhudhau”, “Eeeeggg”, “Chrome”}. Display them in alphabetical order without using library functions .

I'm not very good at coding so i tried doing this using my limited knowledge in the following way:-

#include<iostream>
#include<string>
using namespace std;
string selsort(string s);

string selsort(string s)
{
int i=0,j,k=0;
string min=&s[i];
for(i=0;i<6;i++)
{
    for(j=i+1;j<6;j++)
    {
        if(s[j][k]<s[i][k])
        {
            string *temp;
            min=s[j];
            *temp=s[i];
            s[i]=s[j];
            s[j]=*temp;
        }
        else if(s[j][k]=s[i][k])
        {
                while(k<=s[j].length())
                {
                k++;
                selsort(string s);
                }
             }

        }
   }
     return s;
}

 int main()
 {
     int i;
     string s[6]={"Sdjksajd","Skjdasjj","Bjsdakja","Xhudhau","Eeeeggg","Chrome"};

  s=selsort(s);
  for(i=0;i<6;i++)
  cout<<s[i];
  return 0;
  }

However, i am getting "Error: invalid types 'char[int]' for array subscript" and i think my program needs many more modifications to make it work. How exactly can i solve this question?

The correct answer is "it is not possible to display anything without using library functions". — n. m. could be an AI
– n. m. could be an AI, Commented Nov 8, 2017 at 15:08
While that's true, i think they meant for us to solve it without using library functions to sort or compare the string elements. — Swayam Deep Dash
– Swayam Deep Dash, Commented Nov 8, 2017 at 20:09

Caleth · Accepted Answer · 2017-11-08 14:29:35Z

Whilst the problem specifies that you can't just use a library sort, it doesn't mean that you can't be inspired by a library sort.

template< class RandomIt, class Compare >
void sort( RandomIt first, RandomIt last, Compare comp );

Also note the extra restrictions on RandomIt: it must be ValueSwappable (and dereference to a movable type). Note that a pointer into an array is a RandomIt, and strings are Swappable

So we have two parts:

Compare things
Re-arrange things

For the moment, let's assume that we have a Compare (we will define one later)

Now an obvious property of a sorted collection is that the first element is less than every other element. We can imagine a function RandomIt min_element(RandomIt first, RandomIt last, Compare comp) that finds the smallest element of a range. Thus we can swap the first element with the smallest, then carry on with the rest of the range. Thus sort becomes:

template< class RandomIt, class Compare >
void sort( RandomIt first, RandomIt last, Compare comp )
{
    for (RandomIt it = first; it != last; ++it)
    {
        RandomIt min = min_element(it, last, comp);
        swap(*it, *min);
    }
}

Now we need to implement min_element. We can just go through the range, using Compare to hold onto the current min.

template< class RandomIt, class Compare >
RandomIt min_element( RandomIt first, RandomIt last, Compare comp )
{
    RandomIt min = first;
    for (RandomIt it = first; it != last; ++it)
    {
        if (comp(*it, *min)) { min = it; }
    }
    return min;
}

And also we need swap

template< typename T >
void swap(T & lhs, T & rhs)
{
    T temp = static_cast<T&&>(lhs);
    lhs = static_cast<T&&>(rhs);
    rhs = static_cast<T&&>(temp);
}

Now we have our sorting function, we just need to be able to compare std::strings alphabetically. Luckily for us < is defined for strings to do this, so we just have:

bool string_less(const std::string & lhs, const std::string & rhs)
{
    return lhs < rhs;
}

We can put this all together into

void string_sort(std::string * values, std::size_t count)
{
    sort(values, values + count, string_less);
}

Thanks so much! I solved it with a friend's help. It seems we were missing the string comparison function "bool string_less" which would help in comparing the strings.

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