Nothing

```
globalVariables(c("roads"))
take_a_step = function(paths,roads,blocked = NULL){
#' @title Track one movement
#'
#' @description Track one step of unknown movement by Jack, either on roads or through alleyways
#'
#' @param paths list of all possible paths already traveled
#' @param roads data.frame of non-directional edge pairs for either the road graph or the alley graph
#' @param blocked list of node pairs which cannot be traversed because a police officer blocks it (should not be used for special movement)
#'
#' @return list of all possible paths traveled by Jack
#'
#' @details
#' The non-directional edge pairs are available via \code{data(roads)} or \code{data(alley)}
#' This function does not account for the rule that Jack cannot travel through a road occupied by a police officer.
#'
#' @examples
#' possibilities = start_round(64)
#' possibilities = take_a_step(possibilities,roads)
#' possibilities = take_a_step(possibilities,roads,blocked=list(c(63,82),c(63,65)))
#' possibilities = take_a_step(possibilities,alley)
paths = lapply(paths,gen_possibilities,roads=roads,blocked=blocked)
paths = unlist(paths,recursive = FALSE)
return(paths)
}
take_a_carriage = function(paths){
#' @title Track carriage movement
#'
#' @description Track two steps of unknown movement by Jack, on roads
#'
#' @param paths list of all possible paths already traveled
#'
#' @return list of all possible paths traveled by Jack
#' @examples
#' possibilities = start_round(64)
#' possibilities = take_a_carriage(possibilities)
data(roads,envir = environment())
paths = take_a_step(paths,roads)
paths = take_a_step(paths,roads)
paths = Filter(function(x){rx = rev(x); rx[1] != rx[3]}, paths)
return(paths)
}
trim_possibilities = function(paths,node){
#' @title Trim possible paths
#'
#' @description Remove known impossible end points for Jack, typically as a result of having found, but not arrested Jack.
#'
#' @param paths list of all possible paths already traveled
#' @param node vector of length 1 or 2 which specifies blocked nodes due to the presence of a policeman
#'
#' @return list of trimmed possible paths traveled by Jack
#' @examples
#' possibilities = start_round(64)
#' possibilities = take_a_carriage(possibilities)
#' possibilities = trim_possibilities(possibilities,82)
#' possibilities = trim_possibilities(possibilities,c(66,67))
keep = unlist(lapply(paths,function(x){!identical(sort(rev(x)[seq_along(node)]),sort(node))}))
return(paths[keep])
}
gen_possibilities = function(path,roads,blocked = NULL){
start = rev(path)[1]
p = unique(unlist(roads[roads$x == start | roads$y == start,]))
p = p[p != start]
full_paths = lapply(p,add_possibilities,path=path)
if(!is.null(blocked)){
r = lapply(blocked,trim_possibilities,paths=full_paths)
full_paths = Reduce(intersect,r,init=r[[1]])
}
return(full_paths)
}
add_possibilities = function(p,path){
return(c(path,p))
}
```

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