http://projecteuler.net/problem=14 [Answer:837799]

 

#include <iostream>

using namespace std;

int main()
{
    int longest_chain = 0;
    int number = 0;
    for ( int n = 1; n < 1000000; ++n )
    {
        __int64 tmp = n;
        int terms = 1;
        while ( tmp != 1 )
        {
            if ( tmp & 1 )
            {
                tmp = tmp * 3 + 1;
            }
            else
            {
                tmp >>= 1;
            }
            ++terms;
        }
        if ( terms > longest_chain )
        {
            longest_chain = terms;
            number = n;
        }
    }
    cout << number << endl;
    return 0;
}