function walk_1 ( solution ) {
return frame( range( solution.length * 2 / 3 | 0 ) , 2 ) ;
}
function walk_2 ( solution ) {
return frame( range( solution.length / 3 | 0 , solution.length ) , 2 ) ;
}
function walk ( solution ) {
return frame( range( solution.length ) , 2 ) ;
}