Segment sorting

Question

This is a question from careercup.com. You are given an alphanumeric string. Complete the function sortSegments that will segment the string into substrings of consecutive letters or numbers and then sort the substrings. For example, the string "AZQF013452BAB" will result in "AFQZ012345ABB". The input letters will be uppercase and numbers will be between 0 and 9 inclusive.

#include <iostream>
#include <string>
#include <algorithm>

void sortSegments(std::string& input)
{
    bool toggle1 = isalpha(input[0])? true: false;
    size_t k = 0;
    for(size_t i = 1; i <= input.size(); ++i)
    {
        bool toggle2 = isalpha(input[i])? true: false;
        if(toggle1 != toggle2)
        {
            std::sort(input.begin()+k, input.begin()+i);
            toggle1 = toggle2;
            k=i;
        }
    }
}

int main()
{
    std::string input("AZQKF013452BAB");
    sortSegments(input);
    std::cout << input;
}

Answer 1

FWIW, your function has a bug.

If you change the input string to "AZQKF013452BAB98", you will notice the problem.

The reason for the bug it that the null character is neither a digit nor an alphabetical character.

Here's an updated version of the function that fixes the bug.

void sortSegments(std::string& input)
{
    bool toggle1 = isalpha(input[0])? true: false;
    size_t k = 0;

    // Change the <= to <
    for(size_t i = 0; i < input.size(); ++i)
    {
        bool toggle2 = isalpha(input[i])? true: false;
        if(toggle1 != toggle2)
        {
            std::sort(input.begin()+k, input.begin()+i);
            toggle1 = toggle2;
            k=i;
        }
    }

    // Sort the remaining characters.
    std::sort(input.begin()+k, input.end());
}