学步园

#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:
};