Problem #38

This one was rather simple, I just borrowed a bit of a function I wrote for another problem that required basically the same thing.

#include <iostream>
#include <string>
#include <ctime>
#include <cmath>

using namespace std;

bool isPrime (int);
bool isPentaganal (string);

int main()
{
    clock_t start = clock();
    int total = 0;
    string str;
    char buffer[32];
    int holder = 0;

    for (unsigned int i = 1; i < 1000000; i++)
    {
        str.clear();
        for (unsigned int j = 1; j < 10; j++)
        {
            sprintf (buffer, "%i", i * j);
            str += buffer;
            if (str.size() == 9)
            {
                if (isPentaganal (str))
                {
                    holder = atoi (str.c_str());
                    if (holder > total)
                        total = holder;
                }
                break;
            }
            else if (str.size() > 9)
                break;
        }
    }

    cout << total << endl 
         << "Process took " << (static_cast<double> (clock()) - start) / CLOCKS_PER_SEC << " seconds." << endl;

    system ("pause");
    return 0;
}

bool isPrime (int num)
{
    if (num == 0 || num == 1)
        return false;
  
    if (num == 2 || num == 3)
        return true;

    for (unsigned int i = 2; i < static_cast<int> (sqrt (static_cast<double> (num))) + 1; i++)
        if (num % i == 0)
            return false;
   return true;
}

bool isPentaganal (string str)
{
    bool found = false;
    bool totalFound = true;
      
    totalFound = true;
    for (unsigned int i = 1; i <= 9; i++)
    {
        found = false;
        for (unsigned int j = 0; j < str.size(); j++)
            if (str[j] == i + '0')
            {
                found = true;
                break;
            }
        if (found == false)
        {
            totalFound = false;
            break;
        }
    }

    return totalFound; 
}