andre andre - 3 months ago 23
C++ Question

A Codility test that needs to be solved

I can not understand the question, can someone clarify it a little bit ?

Update : here is my solution using Kadane algorithm but it fails at the following arrays:

Example test: [-8, 3, 0, 5, -3, 12]
WRONG ANSWER (got 17 expected 12)

Example test: [-1, 2, 1, 2, 0, 2, 1, -3, 4, 3, 0, -1]
WRONG ANSWER (got 12 expected 8)

int max_so_far = 0, max_ending_here = 0;

for (int i = 0; i < A.size(); i++)
{
max_ending_here = max_ending_here + A[i];
if (max_ending_here < 0)
max_ending_here = 0;
if (max_so_far < max_ending_here)
max_so_far = max_ending_here;
}
return max_so_far;

Answer

The function can look as it is shown in the demonstrative program

#include <iostream>
#include <algorithm>
#include <vector>

long long int solution( const std::vector<int> &v )
{
    long long int max_sum = 0;

    for ( auto it = v.begin(); 
         ( it = std::find_if( it, v.end(), []( int x ) { return !( x < 0 ); } ) ) != v.end(); 
        )
    {
        long long int sum = 0;

        while ( it != v.end() && !( *it < 0 ) ) sum += *it++;

        if ( max_sum < sum ) max_sum = sum;
    }

    return max_sum;
}   


int main() 
{
    std::vector<int> v = { 1, 2, -3, 4, 5, -6 };

    std::cout << solution( v ) << std::endl;

    return 0;
}

Its output is

9

You can rewrite the function using indices instead of iterators.

As for your function then it is incorrect at least relative to this condition

    if (max_ending_here < 0)
        max_ending_here = 0;

because instead of checking the current element whether it is less than zero the condition checks the current sum of elements.