Day 6 Notebook

input<-read_lines("Day6Sample.txt")
### obstructions go into a dictionary 
### and locate the guard & size of the lab
obst<-dict()
for (i in 1:length(input)){
  xs<-str_locate_all(input[i],"#")[[1]][,1]
  if(length(xs)>0){
    for(j in 1:length(xs)){
      obst$set(str_c(xs[j],"~",i),0)}}
  if(str_detect(input[i],"\\^")){
    guard<-c(str_locate(input[i],"\\^")[1],i)}}
labrows<-length(input)
labcolumns<-nchar(input[i])

Part 1

Follow the path - take in the dictonary of obstructions, guard position, number of rows, and number of columns

find_distinct_positions<-function(o,g,lr,lc){
  ### Vector of visited positions
  visited<-c(str_flatten(g,collapse="~"))
  ### starting direction
  dr<-"U"
  keepgoing<-TRUE
  ### while it hasn't hit the edge
  while(keepgoing){
    ### depending on the direction - if there's something in front, turn right.  if not, move forward
    switch(dr,
           "U"={if(o$has(str_flatten(g+c(0,-1),collapse="~"))){
             dr<-"R"}else{g<-g+c(0,-1)}},
           "R"={if(o$has(str_flatten(g+c(1,0),collapse="~"))){
             dr<-"D"}else{g<-g+c(1,0)}},
           "D"={if(o$has(str_flatten(g+c(0,1),collapse="~"))){
             dr<-"L"}else{g<-g+c(0,1)}},
           "L"={if(o$has(str_flatten(g+c(-1,0),collapse="~"))){
             dr<-"U"}else{g<-g+c(-1,0)}},
           cat("bad direction\n"))
    visited<-c(visited,str_flatten(g,collapse="~"))
    ### check to see if about to run off the edge
    if((dr=="U"&&g[2]==1)||(dr=="L"&&g[1]==1)||(dr=="D"&&g[2]==lr)||(dr=="R"&&g[1]==lc)){keepgoing<-FALSE}}
  
visited<-unique(visited)
length(visited)}

part1<-find_distinct_positions(obst,guard,labrows,labcolumns)
part1

[1] 41

Guard Path for my input

Part 2

My original thought is to re-run this over and over again putting an obstacle in every step along the path; which means I can’t use a dictionary for the obstacles

obvec<-c()
for (i in 1:length(input)){
  xs<-str_locate_all(input[i],"#")[[1]][,1]
  if(length(xs)>0){
    for(j in 1:length(xs)){
      obvec<-c(obvec,str_c(xs[j],"~",i))}}}

And change the pathfinder to use a vector instead and return the steps along the path

fdpv<-function(o,g,lr,lc){
  ### Vector of visited positions
  visited<-c(str_flatten(g,collapse="~"))
  ### starting direction
  dr<-"U"
  keepgoing<-TRUE
  ### while it hasn't hit the edge
  while(keepgoing){
    ### depending on the direction - if there's something in front, turn right.  if not, move forward
    switch(dr,
           "U"={if((str_flatten(g+c(0,-1),collapse="~"))%in%o){
             dr<-"R"}else{g<-g+c(0,-1)}},
           "R"={if((str_flatten(g+c(1,0),collapse="~"))%in%o){
             dr<-"D"}else{g<-g+c(1,0)}},
           "D"={if((str_flatten(g+c(0,1),collapse="~"))%in%o){
             dr<-"L"}else{g<-g+c(0,1)}},
           "L"={if((str_flatten(g+c(-1,0),collapse="~"))%in%o){
             dr<-"U"}else{g<-g+c(-1,0)}},
           cat("bad direction\n"))
    visited<-c(visited,str_flatten(g,collapse="~"))
    ### check to see if about to run off the edge
    if((dr=="U"&&g[2]==1)||(dr=="L"&&g[1]==1)||(dr=="D"&&g[2]==lr)||(dr=="R"&&g[1]==lc)){keepgoing<-FALSE}}
  
  visited<-unique(visited)
  ### return visited to get the path
  visited}

guardpath<-fdpv(obvec,guard,labrows,labcolumns)
### take out the starting guard space
guardpath<-guardpath[which(guardpath!=str_flatten(guard,collapse="~"))]

This is much the same, but returns whether or not the guard is in a loop

guardloop<-function(o,g,lr,lc){
  ### starting direction
  dr<-"U"
  ### create a dictionary of places/direction combos
  beenthere<-dict()
  beenthere$set(str_flatten(c(g,dr),collapse="~"),0)
  keepgoing<-TRUE
  ### while it hasn't hit the edge
  while(keepgoing){
    ### depending on the direction - if there's something in front, turn right.  if not, move forward
    switch(dr,
           "U"={if((str_flatten(g+c(0,-1),collapse="~"))%in%o){
             dr<-"R"}else{g<-g+c(0,-1)}},
           "R"={if((str_flatten(g+c(1,0),collapse="~"))%in%o){
             dr<-"D"}else{g<-g+c(1,0)}},
           "D"={if((str_flatten(g+c(0,1),collapse="~"))%in%o){
             dr<-"L"}else{g<-g+c(0,1)}},
           "L"={if((str_flatten(g+c(-1,0),collapse="~"))%in%o){
             dr<-"U"}else{g<-g+c(-1,0)}},
           cat("bad direction\n"))
    ### check to see if have been in this position before with this direction
    if(beenthere$has(str_flatten(c(g,dr),collapse="~"))){
      loop<-TRUE
      keepgoing<-FALSE
    }else{
      beenthere$set(str_flatten(c(g,dr),collapse="~"),0)}
    ### check to see if about to run off the edge, if so, loop is FALSE
    if((dr=="U"&&g[2]==1)||(dr=="L"&&g[1]==1)||(dr=="D"&&g[2]==lr)||(dr=="R"&&g[1]==lc)){
      keepgoing<-FALSE
      loop<-FALSE}}
  loop}

Finally, check each step in the path to see if it is a loop or not

obplace<-function(o,g,lr,lc,gp){
  obcounter<-0
  for(i in 1:length(gp)){
    ### check to see if this is a loop if you add something into 
    isloop<-guardloop(c(o,gp[i]),g,lr,lc)
    if(isloop){obcounter<-obcounter+1}}
  obcounter}

part2<-obplace(obvec,guard,labrows,labcolumns,guardpath)
part2

[1] 6