Project Euler Problem 38 Pandigital multiples

Pandigital multiples

Problem 38

Take the number 192 and multiply it by each of 1, 2, and 3:

192 × 1 = 192

192 × 2 = 384

192 × 3 = 576

By concatenating each product we get the 1 to 9 pandigital, 192384576. We will call 192384576 the concatenated product of 192 and (1,2,3)

The same can be achieved by starting with 9 and multiplying by 1, 2, 3, 4, and 5, giving the pandigital, 918273645, which is the concatenated product of 9 and (1,2,3,4,5).

What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1,2, ... , n) where n > 1?

C++:

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const long N = 10000;

bool ispandigital(int n) {
    int digits = 0b1111111110;

    while (n) {
        digits ^= 1 << (n % 10);
        n /= 10;
    }

    return !digits;
}

int main()
{
    int val, max=0, j;
    char s[32], t[32];

    for(int i=1; i<=N; i++) {
        s[0] = '\0';
        t[0] = '\0';
        j = 1;
        while(strlen(s) < 9) {
            sprintf(t, "%d", i * j);
            strcat(s, t);
            j++;
        }
        if(strlen(s) == 9) {
            val = atoi(s);
            if(ispandigital(val))
                if(val > max)
                    max = val;
        }
    }

    cout << max << endl;

    return 0;
}