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Comments, because this code does not document itself

Petra Lamborn 3 years ago
parent
commit
760564e79c
1 changed files with 14 additions and 3 deletions
  1. 14
    3
      12.R

+ 14
- 3
12.R View File

@@ -1,29 +1,36 @@
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 library(stringr)
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 library(dplyr)
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+# Make a dataframe of input, with column 2 as the letter and column 3 as the number
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 input <- readLines("input12.txt") %>% str_match("^(\\w)(\\d+)$") %>% as.data.frame(stringsAsFactors = FALSE)
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 names(input) <- c("Orig", "Arg", "Param")
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 input %>% mutate(
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-                 Param = as.numeric(Param),
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-                 angChange = ifelse(Arg == "R", Param, ifelse(Arg == "L", -Param, 0)),
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-                 Angle = cumsum(angChange) %% 360,
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+                 Param = as.numeric(Param), # Make number numeric type
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+                 angChange = ifelse(Arg == "R", Param, ifelse(Arg == "L", -Param, 0)), # Calculate what each R/L does to the angle
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+                 Angle = cumsum(angChange) %% 360, # Calculate running angle, within 0-359
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+                 # Calculate amount to move East, South at each line
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                  MovEast = ifelse(Arg == "E", Param,
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                                   ifelse(Arg == "W", -Param,
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                                          ifelse(Arg == "F", cos(Angle * pi / 180) * Param, 0))),
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                  MovSouth = ifelse(Arg == "S", Param,
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                                   ifelse(Arg == "N", -Param,
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                                          ifelse(Arg == "F", sin(Angle * pi / 180) * Param, 0))),
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+                 # Running tally of position
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                  PosEast = cumsum(MovEast),
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                  PosSouth = cumsum(MovSouth)
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                  ) -> shipsLog
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+# Calculate manhattin distance
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 mandist <- abs(sum(shipsLog$MovEast)) + abs(sum(shipsLog$MovSouth))
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+# Drop stuff from previous dataframe that wont be used this time
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 shipsLog %>% select(Orig:Angle) %>%
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     mutate(
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+           # Calculate the east, south amount being specified by param value
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            tPMovEast = ifelse(Arg == "E", Param, ifelse(Arg == "W", -Param, 0)),
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            tPMovSouth = ifelse(Arg == "S", Param, ifelse(Arg == "N", -Param, 0)),
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+           # Convert to a rotating reference frame according to the angle
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            PMovEast = ifelse(Angle == 0, tPMovEast,
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                              ifelse(Angle == 90, tPMovSouth,
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                                     ifelse(Angle == 180, -tPMovEast,
@@ -32,8 +39,10 @@ shipsLog %>% select(Orig:Angle) %>%
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                               ifelse(Angle == 90, -tPMovEast,
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                                      ifelse(Angle == 180, -tPMovSouth,
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                                             tPMovEast))),
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+           # Calculate running position of waypoint in rotated frame
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            PREastPos = cumsum(PMovEast) + 10,
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            PRSouthPos = cumsum(PMovSouth) - 1,
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+           # Return to original fixed reference frame
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            PTEastPos = ifelse(Angle == 0, PREastPos,
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                               ifelse(Angle == 90, -PRSouthPos,
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                                      ifelse(Angle == 180, -PREastPos,
@@ -42,9 +51,11 @@ shipsLog %>% select(Orig:Angle) %>%
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                               ifelse(Angle == 90, PREastPos,
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                                      ifelse(Angle == 180, -PRSouthPos,
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                                             -PREastPos))),
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+           # Calculate movement of ship at each line
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            ShipMoveEast = ifelse(Arg == "F", Param * PTEastPos, 0),
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            ShipMoveSouth = ifelse(Arg == "F", Param * PTSouthPos, 0)
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            ) -> shipsLog2
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+# Calculate manhattin distance
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 mandist2 <- abs(sum(shipsLog2$ShipMoveEast)) + abs(sum(shipsLog2$ShipMoveSouth))