Function to check if a string contains equal number of one and zeros or not
bool isValid ( string p ) { int n = p . length ( ) ; int c1 = 0 , c0 = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( p [ i ] == '0' ) c0 ++ ; if ( p [ i ] == '1' ) c1 ++ ; } return ( c0 == c1 ) ? true : false ; }