topcoder-srm144-div

#include <string>
#include <vector>
#include <iostream>
using namespace std;

class BinaryCode{
public:
vector<string> decode(string message){

//prepare the basic return value
vector<string> result;
result.push_back( "NONE" );
result.push_back( "NONE" );

if( message.empty() )
return result;

/* set down the value that can be deducted form 0 or 3 */
string module;
for( int i=0; i<message.length(); ++i)
module.push_back( 'x' );

for( int i=0; i<message.length(); ++i ){
if( message[i] == '0' ){
module[i] = '0';
if( i-1 >= 0 )
module[i-1] = '0';
if( i+1 < message.length() )
module[i+1] = '0';
}
else if( message[i] == '3' ){
module[i] = '1';
if( i-1 >= 0 )
module[i-1] = '1';
if( i+1 < message.length() )
module[i+1] = '1';
}
}

/* set down the value can be deducted from 1 or 2 */
for( int k=0; k<=1; ++k ){
if( module[0] != '1'- k ){

string tmp = module;

/* process the [0] unit */
tmp[0] = '0'+ k;

/* process the [1] unit */
char ch = message[0] - tmp[0] + '0';
/*事实上ch可能算出2来，如message="22111",tmp[0]='0'*/
if( ch!='0' && ch!='1' ){
goto nosolution;
}
if( (module[1] != 'x') && (ch!=module[1]) ){
goto nosolution;
}
else{
tmp[1] = ch;
}

/* process [2]..[length-1] units */
for( int i=2; i<tmp.length(); ++i ){
ch = message[i-1] - tmp[i-1] - tmp[i-2] + '0' + '0';
if( ch!='0' && ch!='1' ){
goto nosolution;
}
if( (module[i] != 'x') && (ch != module[i]) ){
goto nosolution;
}
else{
tmp[i] = ch;
}
}

/*add it to the result*/
result[k] = tmp;
nosolution: ;
}
}
return result;
};
private:
};