sequence.cpp(c++11)

# include <stdio.h>
# include <stdlib.h>
# include <iostream>
# include <string>

int str2int( const char s )
{
    return ( s < 'a' ) ? s-'0': s-0x57;
}

void test( const std::string & input, const std::string & ans )
{
    int max_cnt = 1;
    for( const char c1: input )
    {
        for( const char c2: input.substr( input.find_first_of(c1)+1 ) )
        {
            const int diff = str2int(c2) - str2int(c1);
            char pre_c = c2;
            int cnt = 2;
            for( const char c3: input.substr( input.find_first_of(c2)+1 ) )
            {
                if( str2int(c3) == str2int(pre_c)+diff )
                {
                    cnt++;
                    pre_c = c3;
                }
                else if( str2int(c3) > str2int(pre_c)+diff )
                {
                    break;
                }
            }
            if( cnt > max_cnt ) max_cnt = cnt;
        }
    }
    printf("%s\n", (max_cnt == atoi(ans.c_str())) ? "ooooo GOOD ooooo": "xxxxx BAD xxxxx");
}

int main( void )
{
/*0*/ test( "12345abcz", "5" );
/*1*/ test( "012abku", "4" );
/*2*/ test( "01245689cdeghik", "6" );
/*3*/ test( "0", "1" );
/*4*/ test( "m", "1" );
/*5*/ test( "01", "2" );
/*6*/ test( "az", "2" );
/*7*/ test( "0az", "2" );
/*8*/ test( "0ak", "3" );
/*9*/ test( "05ak", "3" );
/*10*/ test( "01349acdrsuv", "2" );
/*11*/ test( "01245789efgipqstux", "3" );
/*12*/ test( "0123456789abcdefghijklmnopqrstuvwxyz", "36" );
/*13*/ test( "02468acegikmoqsuwy", "18" );
/*14*/ test( "0369cfilorux", "12" );
/*15*/ test( "048cgkosw", "9" );
/*16*/ test( "05afkpuz", "8" );
/*17*/ test( "0123456789abcdefghjklmnopqrstuvwxyz", "18" );
/*18*/ test( "0123456789bcdefghijklmopqrstuvwxyz", "12" );
/*19*/ test( "0156abfgklpquv", "7" );
/*20*/ test( "0167cdijopuv", "6" );
/*21*/ test( "0178eflmst", "5" );
/*22*/ test( "0189ghopwx", "5" );
/*23*/ test( "019aijrs", "4" );
/*24*/ test( "012567abcfghklmpqruvw", "7" );
/*25*/ test( "012678cdeijkopquvw", "6" );
/*26*/ test( "012789efglmnstu", "5" );
/*27*/ test( "01289aghiopqwxy", "5" );
/*28*/ test( "0129abijkrst", "4" );
/*29*/ test( "01235678abcdfghiklmnpqrsuvwx", "7" );
/*30*/ test( "01236789cdefijklopqruvwx", "12" );
/*31*/ test( "0123789aefghlmnostuv", "5" );
/*32*/ test( "012389abghijopqrwxyz", "5" );
/*33*/ test( "01239abcijklrstu", "4" );
/*34*/ test( "368acdknouvz", "4" );
/*35*/ test( "369chikmnopqruwx", "6" );
/*36*/ test( "05689cdefghijklmnopqrstvwy", "18" );
/*37*/ test( "2489abdeiklrsuvwz", "4" );
/*38*/ test( "678bhijklnpqrsuvwxyz", "6" );
/*39*/ test( "1246cfjkopquxz", "5" );
/*40*/ test( "123459abcefhilmotuvx", "6" );
/*41*/ test( "02578acdefikmopqsuvwxz", "8" );
/*42*/ test( "135abdefghijlopstuwz", "7" );
/*43*/ test( "0126789fgjnotuvxy", "5" );
/*44*/ test( "2345678defjkmnoqrtvwxy", "7" );
/*45*/ test( "02568bdemnostw", "5" );
/*46*/ test( "145689bdfhilnqrstvwxz", "6" );
/*47*/ test( "4aghjrtuvwxyz", "7" );
/*48*/ test( "158achklmqstwy", "3" );
/*49*/ test( "012346abceghjknortv", "5" );
    return 0;
}