Sort function giving floating point exception for a large input of 0's

Question

I have written a code for this problem:

Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

What basically I am trying to achieve in this code is to use radix sort logic on most significant digit first and arranging it as per decreasing order. Later I am doing for second most significant digit and so on. I have used std::sort() function by passing a vector of pairs, where first of the pair is the value and second of the pair is the index. The following is my code:

bool radixOrder(pair<int,int> p1, pair<int,int> p2)
{
    int val1=p1.first;
    int e1=p1.second;
    int val2=p2.first;
    int e2=p2.second;
    if(val1==val2 && e1==e2)
    {
        return val1==val2;
    }
    else if(((val1/e1)%10) == ((val2/e2)%10))
    {
        while(val1/e1 == val2/e2)
        {
            if(e1/10!=0)
                e1=e1/10;
            if(e2/10!=0)
                e2=e2/10;
        }
        return (val1/e1)%10 > (val2/e2)%10;
    }
    else
    {
        return (val1/e1)%10 > (val2/e2)%10;
    }
}

vector<pair<int,int> > createVNew(vector<int>& v)
{
    vector<pair<int,int> > temp;
    for(int i=0; i<v.size(); i++)
    {
        cout << i << endl;
        int val=v[i], e=1;
        if(v[i]==0)
        {
            temp.push_back(make_pair(val, 1));
        }
        else
        {
            while((e/v[i])==0)
                e*=10;
            if(e!=v[i])
            {
                temp.push_back(make_pair(val,e/10));
            }
            else if(e==v[i])
            {
                temp.push_back(make_pair(val,e));
            }
        }
    }
    return temp;
}

string largestNumber(vector<int>& v)
{
    int e=1;
    vector< pair<int,int> > vnew=createVNew(v);
    sort(vnew.begin(), vnew.end(), radixOrder);
    stringstream s;
    for(int i=0; i<vnew.size(); i++)
    {
        s<<vnew[i].first;
    }
    return s.str();
}

largestNumber(..) is my function which is returning the desired string. Now This code works fine for most non zero inputs that I could try. But when input is a long vector of 0's, something like:

[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]

it is giving floating point exception.

I have tried finding the solution, but havent been able to. I am a beginner in cpp, and any help would be great.

Answer 1

Your radixSort function violates the Compare requirements, namely irreflexivity (that is, radixOrder(x, x) must return false but it returns true because the execution goes to the first if branch).

So you get a classic example of undefined behavior here. I believe that piece of code should be rewritten somehow like

if (e1==e2)
{
    return val1 > val2;
}

^{Though, I would solve the problem just by sorting the input numbers as strings in reverse order.}