CODEWITHSUNDEEP
c++
user6204551
user6204551

Reputation: 1

Sorting C++, First element not working

Please have a look at this code. It's supposed to sort it in non-decreasing order, but for some reason it puts the largest element first then the rest in the correct order. 

int min(int start)
    {
        int minimum = list[start];
        int location = 0;
        for (int i = start; i < size; i++)
        {
            if (list[i] < minimum)
            {
                minimum = list[i];
                location = i;
            }
        }
        return location;
    }

    void sort()
    {

        int minimum;
        for (int i = 0; i < size; i++)
        {
            minimum = min(i);
            int temp = list[i];
            list[i] = list[minimum];
            list[minimum] = temp;
        }

    }

Upvotes: 0

Views: 65

Answers (2)

Remy Lebeau
Remy Lebeau

Reputation: 596352

@Slava explained why your existing code is broken and how to fix it.

I'd like to offer an alternative solution - learn to use standard STL algorithms.

Such as the std::sort() algorithm:

Sorts the elements in the range [first, last) in ascending order

#include <algorithm>

void sort()
{
    std::sort(&list[0], &list[size]);
}

Even if you want to implement your own sort() logic (though std::sort() does allow you to pass in a custom functor to implement custom sorting), your min() function could use the STL std::min_element() algorithm, and your sort() function could use the STL std::swap() algorithm:

#include <algorithm>

int min(int start)
{
    int *found = std::min_element(&list[start], &list[size]);
    return std::distance(&list[0], found);
}

void sort()
{
    for (int i = 0; i < size; i++)
    {
        int minimum = min(i);
        if (minimum != i)
            std::swap(list[i], list[minimum]);
    }
}

Upvotes: 1

Slava
Slava

Reputation: 44258

int location = 0;

you initialize location to 0 and if list[start] is already minimum and start != 0 you return incorrect location. change it to 

int location = start;

or you can use start instead of location:

int min(int start)
{
    for (int i = start + 1; i < size; i++)
    {
        if (list[i] < list[start])
            start = i;
    }
    return start;
}

Upvotes: 0

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