Day 13 Notebook

#input<-read_lines("Day13Sample.txt")
input<-read_lines("../../AoCData/AOC2018/Day13.txt")

Part 1

First read in the input

maze<-dict()
carlist<-list()
for(i in 1:length(input)){
  linei<-input[i]
  for(j in 1:nchar(input[1])){
    x<-str_sub(linei,j,j)
    if(x %in% c("-","|","\\","/","+")){
      maze$set(paste(j,i),x)}
    if(x%in%c(">","<")){
      maze$set(paste(j,i),"-")
      if(x==">"){cr<-list(j,i,"E","L")
      }else{cr<-list(j,i,"W","L")}
      carlist<-c(carlist,list(cr))}
    if(x%in%c("v","^")){
      maze$set(paste(j,i),"|")
      if(x=="v"){cr<-list(j,i,"S","L")
      }else{cr<-list(j,i,"N","L")}
      carlist<-c(carlist,list(cr))}}}

The function to move a car

carmove<-function(c,m){
  ##depends on the car's direction
  nc<-c
  switch(c[[3]],
         "N"={
           x<-m$get(paste(c[[1]],c[[2]]-1))
           nc[[2]]<-c[[2]]-1
           switch(x,
                  "|"={},
                  "\\"={nc[[3]]<-"W"},
                  "/"={nc[[3]]<-"E"},
                  "+"={switch(c[[4]],
                              "L"={nc[[3]]<-"W"
                              nc[[4]]<-"S"},
                              "S"={nc[[4]]<-"R"},
                              "R"={nc[[3]]<-"E"
                              nc[[4]]<-"L"},
                              cat("bad plus\n"))},
                  cat("badN\n"))},
         "S"={
           x<-m$get(paste(c[[1]],c[[2]]+1))
           nc[[2]]<-c[[2]]+1
           switch(x,
                  "|"={},
                  "\\"={nc[[3]]<-"E"},
                  "/"={nc[[3]]<-"W"},
                  "+"={switch(c[[4]],
                              "L"={nc[[3]]<-"E"
                              nc[[4]]<-"S"},
                              "S"={nc[[4]]<-"R"},
                              "R"={nc[[3]]<-"W"
                              nc[[4]]<-"L"},
                              cat("bad plus\n"))},
                  cat(nc[[1]],nc[[2]],"badS",x,"\n"))},
         "E"={
           x<-m$get(paste(c[[1]]+1,c[[2]]))
           nc[[1]]<-c[[1]]+1
           switch(x,
                  "-"={},
                  "\\"={nc[[3]]<-"S"},
                  "/"={nc[[3]]<-"N"},
                  "+"={switch(c[[4]],
                              "L"={nc[[3]]<-"N"
                              nc[[4]]<-"S"},
                              "S"={nc[[4]]<-"R"},
                              "R"={nc[[3]]<-"S"
                              nc[[4]]<-"L"},
                              cat("bad plus\n"))},
                  cat("badE\n"))},
         "W"={
           x<-m$get(paste(c[[1]]-1,c[[2]]))
           nc[[1]]<-c[[1]]-1
           switch(x,
                  "-"={},
                  "\\"={nc[[3]]<-"N"},
                  "/"={nc[[3]]<-"S"},
                  "+"={switch(c[[4]],
                              "L"={nc[[3]]<-"S"
                              nc[[4]]<-"S"},
                              "S"={nc[[4]]<-"R"},
                              "R"={nc[[3]]<-"N"
                              nc[[4]]<-"L"},
                              cat("bad plus\n"))},
                  cat("badW\n"))},
         cat("bad direction\n"))
  nc}

Check to see if any of the things are in the same place

crashed<-function(crs,m){
  ### first, sort the coordinates
  sortcoord<-sapply(crs,function(x){
    paste(sprintf("%03d",x[[2]]),sprintf("%03d",x[[1]]),sep=",")})
  crs<-crs[order(sortcoord)]
  i<-1
  x<-NA
  while(i<=length(crs)){
    ## create a holder for crashed cars
    crashed<-c()
    ## move the car
    crs[[i]]<-carmove(crs[[i]],m)
    ## start checking for cars in the same place
    j<-1
    while(j<=length(crs)){
      ## don't compare to itself
      if(i==j){j<-j+1
      ## if there is a crash, add the compare car to the crash list
      next}else if(crs[[i]][[1]]==crs[[j]][[1]]&&crs[[i]][[2]]==crs[[j]][[2]]){
        crashed<-c(crashed,j)}
      j<-j+1}
    ## if there is a crashed car, add the first car to it
    if(length(crashed>0)){
      x<-c(crs[[i]][[1]],crs[[i]][[2]])
    break}
    i<-i+1}
  x}

findcrashes<-function(cr,m){
  keepgoing<-TRUE
  while(keepgoing){
    ## move the cars - 
    cr<-lapply(cr,function(x){carmove(x,m)})
    ## see if anything crashed
    crashq<-crashed(cr,m)
    ## if so, stop, if not, keep going
    if(!any(is.na(crashq))){keepgoing<-FALSE}}
  ## adjust because it's 1 indexed
  crashq<-crashq-c(1,1)
  ## turn back to a string
  str_c(crashq,collapse=",")}

findcrashes(carlist,maze)

[1] "100,21"

100,21

Part 2

Takes in the car list, but removes any that have crashed

avert<-function(crs,m){
  ## first sort the cars in order vertical then horizontal
  sortcoord<-sapply(crs,function(x){
    paste(sprintf("%03d",x[[2]]),sprintf("%03d",x[[1]]),sep=",")})
  crs<-crs[order(sortcoord)]
  ### find and remove crashes
  i<-1
  while(i<=length(crs)){
    ## create a holder for crashed cars
    crashed<-c()
    ## move the car
    crs[[i]]<-carmove(crs[[i]],m)
    ## start checking for cars in the same place
    j<-1
    while(j<=length(crs)){
      ## don't compare to itself
      if(i==j){j<-j+1
      ## if there is a crash, add the compare car to the crash list
      next}else if(crs[[i]][[1]]==crs[[j]][[1]]&&crs[[i]][[2]]==crs[[j]][[2]]){
        crashed<-c(crashed,j)}
      j<-j+1}
    ## if there is a crashed car, add the first car to it
    if(length(crashed>0)){
      ## for debugging, give the crash coordinates
      cat("crash at ",crs[[i]][[1]]-1,",",crs[[i]][[2]]-1)
      crashed<-c(crashed,i)
      ## remove all crashed cars
      crs<-crs[-crashed]
      ## if only one car left STOP RIGHT THERE
     # if(length(crs)==1){return(crs)}
    next}
    i<-i+1}
  crs}

avoidcrashes<-function(cr,m){
  keepgoing<-TRUE
  tick<-1
  carcount<-length(cr)
  while(keepgoing){
    ### move and remove the cars
    cr<-avert(cr,m)
    ## if only one car left, stop
    if(length(cr)==1){keepgoing<-FALSE}
    if(length(cr)!=carcount){
      cat(" at ",tick,"\n")
      carcount<-length(cr)}
    tick<-tick+1}
  cr<-cr[[1]]
  ## adjust for 0 index
  cr<-c(cr[[1]],cr[[2]])-c(1,1)
  ## turn to a string
  str_c(cr,collapse=",")}

part2<-avoidcrashes(carlist,maze)

crash at  100 , 21 at  303 
crash at  89 , 17 at  441 
crash at  67 , 115 at  476 
crash at  38 , 20 at  1092 
crash at  58 , 149 at  1123 
crash at  52 , 57 at  1209 
crash at  104 , 116 at  7904 
crash at  89 , 121 at  19217 

part2

[1] "113,108"

113,108