navigate_two.tcl

#!/bin/env tclsh

#  ___              _ ___      ___          _     ___
# |   \ __ _ _  _  / |_  )    | _ \__ _ _ _| |_  |_  )
# | |) / _` | || | | |/ /     |  _/ _` | '_|  _|  / /
# |___/\__,_|\_, | |_/___|    |_| \__,_|_|  \__| /___|
#            |__/
#
# "Rain Risk"
#
# Challenge:
# Part Two manipulates a _waypoint_ instead of the ship itslelf except for F.
# New rules:
#
# - Action [NESW] -> move WAYPOINT the given direction by given value.
# - Action [LR] -> rotate WAYPOINT around the ship counterclock/clockwise
# - Action F -> move SHIP forward to WAYPOINT a number of times equal to the
#   given VALUE. (I am still not 100% sure what this means...)
#

# After these steps on the sample, the ship's Manhattan Distance from its
# starting position is 214 + 72 = 286. Report the Manhattan Distance between
# the new location and the ship's starting position.

set file [open "navigation_instructions.txt"]
set route [read $file]
close $file

# Ship starting position, still facing east
set ship(x) 0
set ship(y) 0

# Waypoints are relative to the ship's position
set waypoint(x) 10
set waypoint(y) -1

foreach step $route {
  set mode [string index $step 0]
  set value [string range $step 1 end]

  if {$mode == "F"} {
    incr ship(x) [expr $waypoint(x) * $value]
    incr ship(y) [expr $waypoint(y) * $value]
  }

  switch $mode {
    N {incr waypoint(y) [expr 0 - $value]}
    S {incr waypoint(y) $value}
    W {incr waypoint(x) [expr 0 - $value]}
    E {incr waypoint(x) $value}
    # @TODO: Can these _almost_ identical blocks be consolidated?
    L {
      set rotations [expr $value / 90]
      for {set i 0} {$i < [expr $value / 90]} {incr i} {
        set newX $waypoint(y)
        set newY [expr -$waypoint(x)]
        set waypoint(x) $newX
        set waypoint(y) $newY
      }
    }
    R {
      set rotations [expr $value / 90]
      for {set i 0} {$i < [expr $value / 90]} {incr i} {
        set newX [expr -$waypoint(y)]
        set newY $waypoint(x)
        set waypoint(x) $newX
        set waypoint(y) $newY
      }
    }
  }
}

puts "Final Waypoint: $waypoint(x), $waypoint(y)"
puts "Final Ship Position: $ship(x), $ship(y)"
puts "Manhattan distance: [expr abs($ship(x)) + abs($ship(y))]"
# Part Two solution:
#   Final Waypoint: -85, 31
#   Final Ship Position: -1078, 11307
#   Manhattan distance: 12385